Database Users

Make your own 5V backup battery?

Hey..
I want to make a pretty big backup battery for my TD2 or any other device that charges using a USB port.
I have 8 recharchable AA batteries (1,5V and 1800 mAh each) and want them in pairs off 4.
So two pairs off 6V packs and a total off 3600mAh.
But how do i acctually make this? Because i want to just plug it in some power socket so it will recharge the backup battery..
And when i need it. i just plug my phone in the backup battery so it will recharge and last ALLOT longer.

generally speaking, good socket adapters and car adapters (original ones too) have an automatic switch off when the battery gets fully charged. failing to do so can dramatically reduce the life of your battery. i think a safer (and more elegant too) solution is to buy a spare battery.

Sounds like hard work to me
Would something like this be better, I know its not as powerful as what you are proposing, and it has the cut out built into it as well.
PowerMonkey Classic
or get what I have which is this
Powermonkey Explorer
Highly recommended
PS Topic probably in wrong place, Accessories better place !?!
It charges via USB, mains, solar, has extra connectors for alot of devices.
Just my input...

If it was my problem, I would make a very simple constant current charger using a disused 19V laptop supply (doesn't everyone have one?) and a series resistor. The resistor value should be calculated from the charging current. You shouldn't go for a high current because you would need to cut off the charging when complete, or the cells would get very hot and be damaged. Proper chargers do this, but it takes a relatively complex circuit to manage the charge.
A low charge current (less than a tenth of the cell capacity) is good for cell lifespan and is safe to leave connected for a while even when the charge is complete without damaging the cell. The only drawback is a long charge time. I would select a current which charges fully in about 22 hours, so you put it on charge at a certain time and remove it next day at the same time - easy to remember.
With a 19V supply and a battery pack voltage of about 5 volts, a current of 200mA would need a resistor of value 70 Ohms - the nearest actual value is 68 ohms. Power rating would need to be 3W absolute minimum, try to get a 5W part. Your 3600mA pack should be charged after 22-24 hours. If your old laptop supply is different from 19V, you need to calculate the resistor accordingly. A low voltage supply wouldn't be suitable, because the charging current would vary too much.
Two points: Be sure to get the polarity of the laptop supply correct, and always have the supply connected to the mains when the battery pack is connected to it (otherwise the battery pack will try to put a current back through the supply, which it might not like!). Or you could incorporate a series 1A diode to protect against that happening.
I'm using a very simple supply like this to charge a 5v pack over 24 hours (it's from a bluetooth speaker - the internal charging circuit blew up) and it's perfect - I expect a long lifespan for the cells.
It's worth pointing out that putting 2 banks of cells in parallel, as you intend to, is not ideal unless the cells are matched, but in practice it shouldn't matter much.

there are 5v regulators u can buy to make your circuit work at 5v what is nice about that is that i can step up and step down voltages if the voltage fluctuates(battery power levels), btw the phones do the auto shutoff when the battery is full not the charger, because charger does not have a feedback system to read battery levels. Why do u think there is 3 or some times 4 connections on a battery and not 2
the problems u might encounter are amp levels due to long term charging but 4 1800mA AA battery will do a good charge for your phone
anyway here is a 5v reg from radioshack as referrence
http://www.radioshack.com/product/index.jsp?productId=2062599

jngtt said:
there are 5v regulators u can buy to make your circuit work at 5v what is nice about that is that i can step up and step down voltages if the voltage fluctuates(battery power levels), btw the phones do the auto shutoff when the battery is full not the charger, because charger does not have a feedback system to read battery levels. Why do u think there is 3 or some times 4 connections on a battery and not 2
the problems u might encounter are amp levels due to long term charging but 4 1800mA AA battery will do a good charge for your phone
anyway here is a 5v reg from radioshack as referrence
http://www.radioshack.com/product/index.jsp?productId=2062599
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I might be misunderstanding you, but if you mean charging the cells from a 5v regulator, that would be a bad idea. NiCad or NiMH cells shouldn't and can't be charged from a constant voltage source. When you start charging the current would be too high (the 7805 would probably switch itself off) and the charge would never finish either, as 4 cells in series have an endpoint voltage of about 5.6 - 6.0V.
But perhaps you didn't mean that... (in which case apologies for butting in)

Pete_S said:
I might be misunderstanding you, but if you mean charging the cells from a 5v regulator, that would be a bad idea. NiCad or NiMH cells shouldn't and can't be charged from a constant voltage source. When you start charging the current would be too high (the 7805 would probably switch itself off) and the charge would never finish either, as 4 cells in series have an endpoint voltage of about 5.6 - 6.0V.
But perhaps you didn't mean that... (in which case apologies for butting in)
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The 5v regulator just sets the voltage to be 5 volts as with all usb ports and usb chargers, the HTC charger that comes with the phones pushes 2A, the usb ports on our PCs pushes 0.5A. Ampere is just current, if u think that is too much amps u can put a fuse. This is the first time someone told me constant is bad
btw do u know how cells and battery work?

Going back to the original post, Overloaded just wanted a way to recharge his proposed battery pack from the mains, if I read it correctly.
I don't see where a 7805 5V regulator fits into this, either for charging the phone (the battery pack is 5-6V and the 7805 needs at least 7V to function) or for charging the battery pack (for reasons I've already outlined).

u are right, he does not need the 5v reg, infact all he needs to do is put the battery in serise with a diode to prevent feedback and he should be fine

Slightly off topic,
I recently got hold of two 11v LiPo packs, a regulator, a fast charger and all the cable and connectors to buils a 4400 mAh power souce. At 5v this gives circa. 8800 mAh. I bought it in a model shop sale and I've wanted to play around with the setup for some time.
The two packs are to big, but one on it's own is not too bad. And they were cheap!

USB/AC Charging Discussion

Decided to make a seperate thread for this. Maybe a mod could move those posts over...
scoob8000 said:
This is very interesting.. Gonna order one of those adaptors. I have another possible source that I'll call and see if they can get them.
Dx rocks but I lack the patience to wait for overseas shipping.
Food for thought..
I have a cheapo 4 port usb hub on my night stand for charging all my devices. It is limited to 500ma per port. Ive noticed it won't charge my atrix. Guessing 500ma isn't enough..
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Rred said:
scoob-
"It is limited to 500ma per port. Ive noticed it won't charge my atrix. Guessing 500ma isn't enough.."
No, physics doesn't work like that. If the VOLTAGE from your USB device is above the charging voltage for the phone, even a 100mA charger would be enough to charge the phone up. It would just take a long time, perhaps 22-24 hours to do so.
The normal Moto chargers are about 1000mA and they charge the phone quickly, usually two hours or less. But Moto has been making very generous chargers for years, they even supplied a 1000mA charger with my bt earpiece, which doesn't need that much power at all.
If a 500mA charger hasn't fully charged your phone in 4 hours, there's something else wrong. Bad wire, bad contact, not plugged in tight...or the "Made in China" effect.<G>
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_Dennis_ said:
No you are wrong sir. The phone will not charge on a 500 ma charge. It will use less battery but 500ma charger is not sufficient to both power the device and charge it. Also the charger supplied it 750ma charger and if you are running 1.2.6 the phone will refuse 1a chargers. Just because something provides voltage in the correct range does not mean ut provides enough energy to charge something else. Voltage is potential current is actual power. Just plug your phone into a USB socket without the computer having drivers (there by limiting the socket to 500ma) it won't charge.
Sent from my MB860 using Tapatalk
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scoob8000 said:
Sorry OP for the threadjacking..
I'm familiar with Ohm's law, where I was headed is I think the phone may be doing one of two things. (purely guessing )
It may just be adhering to USB specs. It realizes the hub is a USB device and not just a charger. Since there is no computer on the other side, to negotiate more than 100ma it just doesn't charge.
Or the voltage drop @ 500ma (my hubs max per port) is just too high to enter charging. Worth noting, is when the battery is >90 and I plug the hub in, the notification led lights, but the battery still discharges.
I need to hack up a usb cord to take some voltage/current measurements. Maybe I'm just being OCD, but I like to "slow charge" my devices while I sleep.
[edit] I think I'm going to try making a charge only USB cable... That might answer some questions
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Rred said:
Dennis?
"It will use less battery but 500ma charger is not sufficient to both power the device and charge it."
Powering the phone, and charging the phone, and simultaneously doing both, are three different things.
The 500mA is sufficient to CHARGE the phone, that's all I said. I have no idea how much power it takes to POWER the phone with all four radios (BT, GPS, Wifi, cellular) active and music or Angry Birds playing at the same time. The power drain for each of those may be significant.
But since the phone has a ~1900mAh battery, you can establish the phone's power drain by turning on "everything" and letting the battery drain from full charge. If it takes four hours to go dead...yes, the phone may consume 500mA all by itself, leaving nothing to charge the battery. Again, that's physics, and it applies the same way to every laptop and phone on the market, and other devices that use adapter/chargers.
I stand by what I said: 500mA will fully recharge the battery in about 4 hours. I did NOT say it would power all four radios and play music as well as charging the phone at the same time. You'll have to do your own math to find that out, but the physics remains the same. My phone usually charges while I sleep, and a 500mA source will do that very nicely, with just the cellular radio enabled, and not in conversation.
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So I just made a little USB breakout cable so I could do a little investigation..
Oddly, even with the stock charger and the data lines disconnected the Atrix will not charge. I'm supecting most AC chargers must supply power on the data lines as well, or do something with them that triggers the device to charge.
As for the voltage, my hub and oem charger both throw out 5.12v with no load. When I plug the phone in, there is no drop at all.
From what my googling turns up, I may need a 180ish ohm resistor between the data lines. The phone looks for that to enter charging mode. Apparently this is why the drivers are needed for charging on some computers. Instead of resistance, it gets the charge signal from the pc.
So anyway out of curiosity I also took a few load readings:
Battery at 40%, screen off, phone idle: 600~ma
The most I could get it to pull was with battery at 40%, streaming last fm over a BT headset, and running quadrant. I saw around 690ma at peak.
Voice calls don't seem to make much of a difference. 10-15ma.
I'm going to check again with a full battery once it's charged. That ought to tell us what the phone itself is using.

I'm using a 550ma 5v charger because it has a longer reach. I stream music, cruise the net, watch videos and it charges my phone no problem.
Sent from my MB860 using XDA Premium App

So with a completely full battery:
Idle, screen off: 100~ma
full load (same as before): 400ma at peak

Either I am lucky and got a better one, or everyone else is wrong on the standard charger. Mine is 850ma. Also, my phone will charge on USB 2 (500ma) if screen is off and I do not use the phone. It's slow but it charges. On USB 3 it charges about half the speed it does on mains.
Sent from WinBorg 4G via XDA premium app

scoob-
"As for the voltage, my hub and oem charger both throw out 5.12v with no load."
Were you using a lab calibrated voltmeter? <G>
Most digital multimeters have a stated accuracy something like 1/2 to 1% on the DC voltages, and then they also have a "float" of 2-4 LSD meaning, the least significant digit (the rightmost one on whatever scale) may float by 2-4 digits.
So on a typical meter where you have a choice between a 2.000 volt scale, and a 20.00 volt scale, "_5.00" on the display could just as easily read "5.05" if it is was 1% off, within the limits of accuracy. And then 5.05 could read 5.09 or 5.00 as the digits float. The errors sometimes cancel out, sometimes accumulate.
I've seen much worse as they get old and out of calibration, where a "12.00" volt reading on one meter was 12.3 on another.
Which is just to say that 5.12 might actually be 5.00, or whatever the USB spec actually calls for. (It doesn't have to be 5.00 exactly.)
I had no idea they needed a signal voltage (available from the data lines on microUSB but not miniUSB) to enter charge state. That "should" mean that you can't use a miniUSB charger with a micro adapter for simple charging. I'll have to try that to see what happens. [ [LATER] Nope, something's not right about needing the signal resistor, because I just charged my Atrix using a miniUSB charger (no data signal possible) with a mini-to-micro power tip adapter, which "should" not be presenting any signal, just passing through the 4 old style connections. ]
There will still be simple--if unpublished or poorly documented--rules of physics governing what happens. Battery charging isn't rocket science, although battery chargers are sometimes "smarter" than rockets are.<G>

CaelanT,
Mines also 850ma..
Rred,
I actually splurged on a very (I think) good meter a few years ago. It's a Fluke 187. They claim .025% DC accuracy. Granted, I've had it a few years and never sent it back in for calibration.
I actually found two sides to having a resistor in the connector.
One story starts with Motorola trying to enforce people using only "genuine" chargers. Link
The other points to the data lines being shorted to indicate to the device that it is a dedicated charging device. Link Skip to the last paragraoh on this page. It's very long winded.
I actually tore apart a old car charger, in the mini usb plug there lied a small resistor between the data pins. I didn't believe how simple it was until I saw it.
Pretty interesting stuff. For us geeks anyway.

scoob, a Fluke is like a Rolls-Royce, except it is more reliable.<G>
The resistors are documented as part of the microUSB spec, they are what are often called "pull-up resistors", i.e. the voltage they provide to the fifth wire "pulls up" the voltage on that line and the tiny brains see that as a signal to do something specific.
Even the Palm Treos used this system. Not on the power line, but on the audio jack. they use a single 3-wire 2.5mm standard minijack and depending on the impedances that they see on it, they will provide mono audio, stereo audio, or mic input plus mono audio, so that three types of devices all plug into the same plug--but all three are sensed and work differently. As Arthur Clarke said "Any sufficiently advanced technology will be indistinguishable from magic."
There's no Moto conspiracy to the resistors, the new microUSB spec provides magic and the industry just doesn't want to bother our pretty little heads by talking about it in any detail.
Now, why Moto omitted the call audio routines from the library on these phones...THAT'S probably a conspiracy.<G>
I'm not reading all 480+ pages of the final USB3 spec, but it appears to refer to standard devices as consuming one "unit" of power at 150mA, with a maximum of six "units" or 900mA, and a maximum voltage of "5" which would mean that if Moto is supplying 5.12V @ 1000mA...they've exceeded the spec and aren't entitled to use the USB logo.
But if they'll fix my call audio library, I won't tell a soul about that.<VBG>

[Q] cheap battery questions

Hello,
i ve been searching for a way to extend the autonomy on the a501.
do you think i can use a cheap 12V lithium battery to charge it or take over when the internal battery is depleted ?
i m not very knowledgeable in electronics, i wouldnt want to damage the internal battery.
there seem to be very few commercial products that would fit this tablet and i m not really interested. i dont have 50$ for a +2h battery life --;
i was thinking of buying a 12V 5000mAh something battery from china and solder the appropriate DC connector on it, but im wondering if there are issues like, the Current needs to be stable at 1,5A or i might reduce the internal battery durability, things like that.
can anyone answer that ?

It's more complicated than that. The power supply probably has a circuit to regulate the flow of energy to the tablet, perhaps the tablet itself also has a circuit that works together, I don't know.
Short answer: buy a second power adapter

There are backup battery/chargers. Scosche goBAT for example.
Just Google around to find the best fit for you.

GullyFoyle said:
There are backup battery/chargers. Scosche goBAT for example.
Just Google around to find the best fit for you.
Click to expand...
Click to collapse
How would that work? Does the goBAT include a charging tip compatible with the A500?

Hello,
thanks for dropping by
its not helping really this is bs
power cat you say "probably" regulates the current. yes that is what i wrote that is what i hoped someone would clear up for me. i dont see how buying another wall charger is going to help me extend the tablet autonomy i would just as well carry the original one around.
gullyfoyle same sideways reading of the OP i would not pay 80$ for a marketed battery/charger.
i hope there are still people out there who can give an educated answer :/
this guy for example http://www.youtube.com/watch?v=LqxhEkDGkbg he says he learned it the hard way (bricked his phone?) because he put 4x(1.5V?) batteries to charge his iphone without the resistors (to get the voltage from 6V down to 5V?)
so there again, can there be issues with the discharge current rate or is it something about lithium batteries behaving differently from alkaline ones ?
i think i ll go ahead and try anyway. worst case scenario the battery will just sit there not putting out anything.

Why wouldn't you pay $80 for a backup battery charger. It was just an example. I'm sure you can find one cheaper after Black Friday, or even with a bit of Googlefu.
We aren't talking about normal chargers but portable charge devices.
http://www.scosche.com/consumer-tech/product/2073
For anyone in need of extra power, the goBAT II provides an innovative solution to the dreaded ‘low battery’ warning. The goBAT II is a powerful backup battery and dual port charger for your mobile devices. The internal 5000mAh ion battery will keep your devices going long after they normally would.
Advantages and Applications
A drained iPhone 4 can be charged 2.6 times with a fully charged goBAT II. An iPad can be charged up to 55% of full charge. This is the ideal battery for long commutes, airport travel and camping.
The goBAT II provides 2 USB charging ports that can be used at the same time. A 2.1 Amp port gives you the ability to charge mobile devices including tablets (iPad and Samsung Galaxy Tab). An additional 1.0 Amp port lets you charge your additional devices (iPhone, iPod, etc.).
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Remember this is JUST AN EXAMPLE. The idea is to show these devices exist and are available for purchase.
http://www.engadget.com/2011/02/23/scosches-gobat-ii-portable-battery-pack-handles-two-usb-devices/
We'll just keep it real simple for you: the object you're looking at above is the Revive II charger, but slimmer, and with a rechargeable battery pack thrown in rather than a wall / cigarette adapter. Got it? Good. The goBAT II contains a 5000mAh rechargeable lithium ion battery, and it offers a pair of USB ports for charging. One's a 10-watt (2.1 Amp) port capable of handling high-maintenance devices like Apple's iPad, while the other is a more conventional 5-watt (1 Amp) socket. Scosche is also throwing in a USB adapter for the Galaxy Tab, theoretically letting those with divided households charge both an iOS and Android tablet at the same time. Brain melting, we know. It also works with the company's Revive charging app, which indicates how long a device will take to charge on any of Scosche's chargers and can also be configured to send an email notification once a device has been fully charged. She's all yours down at the source link for $89.99
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See, others deem it "BRAIN MELTING".
And the cost of that type of thrill is reasonable, for the job it does.
But I can understand how someone would encourage another person to experiment with the guts of electronics they don't fully understand. Screw it up and you can always buy a new one.
Then again, you could buy three or four Gobats and save all the fuss and bother.

mr.bryce said:
Hello,
thanks for dropping by
its not helping really this is bs
power cat you say "probably" regulates the current. yes that is what i wrote that is what i hoped someone would clear up for me. i dont see how buying another wall charger is going to help me extend the tablet autonomy i would just as well carry the original one around.
gullyfoyle same sideways reading of the OP i would not pay 80$ for a marketed battery/charger.
i hope there are still people out there who can give an educated answer :/
this guy for example http://www.youtube.com/watch?v=LqxhEkDGkbg he says he learned it the hard way (bricked his phone?) because he put 4x(1.5V?) batteries to charge his iphone without the resistors (to get the voltage from 6V down to 5V?)
so there again, can there be issues with the discharge current rate or is it something about lithium batteries behaving differently from alkaline ones ?
i think i ll go ahead and try anyway. worst case scenario the battery will just sit there not putting out anything.
Click to expand...
Click to collapse
You will break your tablet.
The charger contains a complex integrated circuit. Sticking on a few resistors isn't gonna do ****.
Look at this for example, a simple wind generator has a complex charging circuit to regulare all the power:
http://www.instructables.com/id/How...nd-turbine/step8/Build-the-charge-controller/
Just google "how to make a charge controller" it's really not as simple as you think.
Quote from the site:
The general principal behind the controller is that it monitors the voltage of the battery(s) in your system and either sends power from the turbine into the batteries to recharge them, or dumps the power from the turbine into a secondary load if the batteries are fully charged (to prevent over-charging and destroying the batteries).

ok thanks ^^
now i understand that part
Short answer: buy a second power adapter
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you are saying the overcharge controller (and other safety features) are all in the wall charger and are not integrated in the tablet.
so if i really really wanted to try i could plug any battery between 12 and 24V to this little guy couldnt i ?
http://www.ebay.ca/itm/220826123824#ht_3149wt_1163

As far as I know...as long as the voltage is correct (eg 12 volts) and the power adapter can produce the required amperage (1.5A) then the tablet will only take the current it can use.
So even if the power adapter is capable of producing 10A say, it doesn't mean it's forcing the 10A onto whatever is connected to it. If you use 1.5A (and if there was a way to connect multiple devices to it) you would still have 8.5A of current you could still take.
Oh the charge regulator would not be in the power adapter, that would be a very stupid design. It would be in the tablet it self to regulate how much charge it requires. I don't know of any power adapter that takes feedback from what it's charging to regulate the current.
It's the same with laptops, that's why you can buy universal laptop chargers when the one you have breaks, you just need to make sure it can supply enough amperage to power your device.
The power adapter is just a simple device that converts 110-240v 50/60hz voltage to 12v and upto whatever amperage it is designed for.
Power plugs in the house are designed at 110-240v to a maximum of 2400W (so ~20a for 110v and 10a for 240v) do you think whatever you plug into it uses up 2400W of electricity at once? No, it just takes what it is required (amperage), that's why you can plug a power strip with like 2-10 additional plugs without any problems unless if try to take more than 2400W in total.
Basic high school physics should of taught people this.

first sensible answer i get thank you daemos i m just not gonna take any chances considering the lithium technology and the fact they could use a "stupid design" for shorter gadget lifespan. if anyone has ever modded a car charger i d love to read about it.

mr.bryce said:
first sensible answer i get thank you daemos i m just not gonna take any chances considering the lithium technology and the fact they could use a "stupid design" for shorter gadget lifespan. if anyone has ever modded a car charger i d love to read about it.
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Lithium ion batteries must be charged at a very specific voltage. So all charging regulation mechanisms would need to be inside the tablet.
I'm pretty sure the ones inside the tablet are definately below 12V so anyone thinking that the AC adapter has any fancy mechanisms to detect feedback, and regulate charge and control the voltage given to the Li-ion cells is incorrect.

Is it safe to use one of THESE to charge or run the tablet?
They also have a 6800mAh ver.

WOW YOU MEN Complicate everything
SIMPLE EASY .. Look at the output voltage of the the power brick for the iconia.. the part that you plug into the wall..
got something that OUTPUTS 12V AT 1.5 AMPS and you are done.. the Li Batteries as in all LI BATTERIES HAVE THERE OWN charging regulators in them.
The reason for this is because if a Battery is drained to a low state it will GET HOT AND OVERHEAT.. NI-CD Batteries can take and handle this heat.. Li batteries become a mini bomb at these temps.. So the are self regulating.. This can be proven by getting a cordless drill hold the shaft from running.. the drill will heat up the battery the device will STOP FUNCTIONING.. Remove the battery and put it back in . it will work again..
Now with that said.. most Li devices say make sure you have 20% or more battery life before flashing and so on.. This is because the DEVICE WILL NOT RUN On the power port. the port only connects to the battery. and in some cases the display lighting.. My cell is this way. if i run the battery until its dead or using gps on it. it will drain the battery faster then it can charge . causing it to not work until you charge it for 5 minutes or so.. this would assume that using a external battery to charge it .. the external batteries themselves would need to be more then 12 volts and atleast double the amps.. then regulated to the 12v 1.5 amps . think of this like pooring water thru a funnel.. to maintain the 12v 1.5 amps. You can test my theory by taking the battery out of your cell phone and trying to run it just on the power adaptor only.. I KNOW MINE WILL NOT RUN.. however if it has older battery technology it will..

[Q] connectiong external battery directly to internal one.

Is it possible/safe to connect an external battery of same voltage but different mAh directly to the internal battery of a tablet to raise its mAh?
I am thinking about moding a tablet case to have a built in battery pack for my Iconia a500 tablet. I can easily squeeze 4 cell phone batteries in between the folds and make two 3.6v 3000mAh(or higher) battery pack with out adding much bulk or weight to it. can probably squeeze a usb hub in there too while i am at it.
I looked at the internal battery and it looks like i can splice its wires and add a connector to hook to the two 3.6v packs for easy connection.
I don't know much about electronics, but from my limited knowledge and layman point of view, as far as the tablet is concerns, it will just have a higher capacity battery, wont it?
can it be done safely without any other electronic components?

I'm not expert in that matter, but I think there's LiIon battery, and AFAIK it may make some confusement to your Fuel Gauge IC and Battery Charging IC, as these are probably calibrated to work with that certain battery type and capacitance. But I don't believe it may damage something if you connect it paralelly.

I would be careful with that if I were you. While it seems simple enough, batteries are much more complex than just voltage and capacity.
Most of the time, external batteries just go through the charging connection of the device so it can handle the power itself. If you connect it directly, you may bypass some part of the charging circuit (often times there's a circuit in the battery itself). Basically, I'm thinking the batteries may not fully charge or one will overcharge. It really depends on how it's set up. I'm not an expert with the design of rechargeable batteries though, so it may be safe.
In short, I would suggest connecting the batteries to the charger to extend your battery life. I'm sure others can offer additional insight.

A good read about batteries: http://batteryuniversity.com/learn/article/serial_and_parallel_battery_configurations
I can't comment on if it will work or if it is safe..

cellphone batteries have a built in protection to prevent them from overcharging or discharging, don't they?
The problem i have with connecting to the charging port is that it needs 12v. connecting 3 or 4 of battereis will give me either too little or too much volt. cant get 12v out of 3.7v batteries with out some kind of additional electronic parts to regulate the voltage. I don't have the sufficient knowledge to do that. this is why i figured ill do it directly. And charging would be simpler too if i can use the charger to charge both the internal and the external batteries at the same time.
Was hopping to hear from someone who did that already. I guess no one is brave/dumb enough to try it.

Sounds intresting looking forward for it

In a "perfect" environment this would be possible.
The inner resistance and voltage difference of the different batteries would even out the different capacity while charging.
You can avoid having these currents between the batteries by using diodes to separate the charging currents.
However my recommendations in terms of reliability, safety and efficiency is to use two or more batteries with the same capacity and dis-/charging curve.

is it the phone or the battery that cuts current when the battery is fully charged?

ridethisbike said:
is it the phone or the battery that cuts current when the battery is fully charged?
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On most phones tablets etc. it's the device that cuts off the charging current when the battery is fully charged.
However nearly ever batteries has also a protection circuit that cuts off the battery in case of
under, over voltage and over current, sometimes even over temperature.

samotronta05 said:
On most phones tablets etc. it's the device that cuts off the charging current when the battery is fully charged.
However nearly ever batteries has also a protection circuit that cuts off the battery in case of
under, over voltage and over current, sometimes even over temperature.
Click to expand...
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ah, well it seems to me that if the battery has to take action, then you're doing it wrong.
I'm not sure exactly how diodes work so I can't comment on that, but definitely use like batteries (two 3000mAh batteries as opposed to one 3000mAh and one 3600mAh) as to not confuse the device about the charge, causing the 3600 to not get fully charged. just make sure they get connected properly (in parallel) and it should work just fine.
in reality its no different than someone using 4 car batteries to power their car audio system. as long as its done properly (in parallel), there is really no harm.

I wouldn't recommend it. While technically it is something that you can do like other posters have said the internal power system is configured in a particular matter. It is likely that the regulation and protection are minimal if they only expect the internal battery. There is also the issue of charging, if you did as you say, you would be discharging the batteries into each other if they weren't exactly at the same levels. So this isn't the recommend method.
What I would recommend you do is put them together so you get something over six volts (two 3.6V packs in series) and put a 5V regulator on it. Then connect it to a USB cable and charge through there. That way you utilize the systems built in protection, aren't messing with the battery connections and can swap it in much easier.

You can... as far as u meet these requirements.
1) notice ur original battery voltage..
2) buy some same kind of them, or u may use others, provided the voltage is same. If u can find higher watt-hour( current) battery of same voltage, go for it.
3) never mix up different amp/ voltage rated batteries together. Ie if u have 3.7v 3200ma batt, and planning to add one more batt in parallel to it go for another 3.7v 3200ma , and not 3.7v 1500ma or 3.5 v 3200ma batt.
4) if u cant find a higher capacity batt of same voltage, go for parallels. Ie join together the positives of two or more batt, and also join together their negatives too.. connect it to the batt terminals of tab,
5) no problems will be caused if u use high current batt, provided u have suited the correct voltage. In ur case u have to ensure proper voltage only. And current can increase to any value.. the system takes only what its needed.
6) the sad thing is it will take more time for charging. But never try to increase the charging current. It will damage the power section. But increase ur patients. Most of the tabs got 1-1.5 amp charger. Never increase the limits.
U may go for it. If u can manage these...
Sent from my HD2 using XDA App

giritrobbins said:
I would recommend it. While technically it is something that you can do like other posters have said the internal power system is configured in a particular matter.
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Yes, to charge with a constant current until a certain voltage is reached.
giritrobbins said:
There is also the issue of charging, if you did as you say, you would be discharging the batteries into each other if they weren't exactly at the same levels.
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Yes, this is the main problem and it's also the reason i recommended using two batteries with the same capacity. Otherwise the constant charge and discharge depending on the size of the difference between the batteries makes the system very inefficient.
giritrobbins said:
What I would recommend you do is put them together so you get something over six volts (two 3.6V packs in series) and put a 5V regulator on it. Then connect it to a USB cable and charge through there. That way you utilize the systems built in protection, aren't messing with the battery connections and can swap it in much easier.
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Which would make it even more inefficient.
showlyshah said:
3) never mix up different amp/ voltage rated batteries together. Ie if u have 3.7v 3200ma batt, and planning to add one more batt in parallel to it go for another 3.7v 3200ma , and not 3.7v 1500ma or 3.5 v 3200ma batt.
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You can mix up different batteries when the voltage is the same, however this is not a the recommend way, since you will not encounter much gain in capacity.
The in terms of capacity smaller battery will be charged by the bigger one all the time.
However if you say i don't care about the efficiency then you can mix up for e.g. a 3.7v 3200mAh and a 3.7v 3000mAh battery.

samotronta05 said:
Yes, to charge with a constant current until a certain voltage is reached.
Yes, this is the main problem and it's also the reason i recommended using two batteries with the same capacity. Otherwise the constant charge and discharge depending on the size of the difference between the batteries makes the system very inefficient.
Which would make it even more inefficient.
You can mix up different batteries when the voltage is the same, however this is not a the recommend way, since you will not encounter much gain in capacity.
The in terms of capacity smaller battery will be charged by the bigger one all the time.
However if you say i don't care about the efficiency then you can mix up for e.g. a 3.7v 3200mAh and a 3.7v 3000mAh battery.
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The issue when you connect them like that will always occur when they are in parallel (you need to add some logic or some diodes in there). Using the same ampacity battery will mitigate it to a point but the internal resistance of a battery will dictate how fast it drains down.
As for the charging, that isn't what i am saying. The internal circuitry that he cannot change is expecting a certain battery with certain characteristics. Putting a second battery in there in parallel will potentially mess with that stuff. If it doesn't realize the size of all the attached battery it will register a fault because it won't be charging correctly.
He isn't going for efficiency here. And a linear regulator is easy, if we want efficient we can do that too. I was just suggesting an alternative that could be easily done.
And the most important point is not about voltages but about chemistry. Different chemistry have different voltages and different knees where they drop suddenly.

The original battery is 7.4v 3350mah. and the charger is 12v 1.5a.
so matching or passing that with batteries I can fit in the space I want it to fit in is a problem.
I was going to use 4 i9000 1500mah batteries, which would fit perfectly, to make a 7.4v 3000mha. but that would be lower then the original. i guess i can try to find higher capacity batteries that i can fit in the case
But if i understand it correctly, the current will keep flowing from the larger capacity battery to the lower one, it will keep them at 100% until the original will drop to lets say 3000mah and then they will all drain at the same rate until they are all empty. and when i charge them, the charging circuitry will get its information only from the original battery, so it will keep charging until the original is full. it may not be as efficient, but it should still get me a significant boost, wouldn't it.
I suppose I could connect them all to make a 14.8v 1500mha with a 12v regulator and use the charging port, but that will leave me with the problem of charging the external pack. no idea how to do that. how do i cheaply and safely charge a 14.8v battery pack?

ronkoni said:
The original battery is 7.4v 3350mah. and the charger is 12v 1.5a.
so matching or passing that with batteries I can fit in the space I want it to fit in is a problem.
I was going to use 4 i9000 1500mah batteries, which would fit perfectly, to make a 7.4v 3000mha. but that would be lower then the original. i guess i can try to find higher capacity batteries that i can fit in the case
But if i understand it correctly, the current will keep flowing from the larger capacity battery to the lower one, it will keep them at 100% until the original will drop to lets say 3000mah and then they will all drain at the same rate until they are all empty. and when i charge them, the charging circuitry will get its information only from the original battery, so it will keep charging until the original is full. it may not be as efficient, but it should still get me a significant boost, wouldn't it.
I suppose I could connect them all to make a 14.8v 1500mha with a 12v regulator and use the charging port, but that will leave me with the problem of charging the external pack. no idea how to do that. how do i cheaply and safely charge a 14.8v battery pack?
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Hey why are u going to make a 14.8v batt pack when urz original ones are 7.4??? I dont realy understand the logic. If u have extra batt, then make the pack like this
Batt pack of 7.4v × 2 and connect them in parallel, thatz all, no need to modify charging circuits, no need to regulate the voltage, and no loss in voltage/ current,
But if u make a high voltage pack, u have to regulate the o/p with some ic, and in turn u will suffer some v/c drop.
Sent from my HD2 using XDA App

i like to connect directly to the battery, but some seem to believe it is not wise if the mAh of the original is higher then the external pack.
The 14.8v pack with a 12v regulator option is for use with the tablet's charging connector which require 12v . A safer option, but leaves me with the charging problem.

ronkoni said:
i like to connect directly to the battery, but some seem to believe it is not wise if the mAh of the original is higher then the external pack.
The 14.8v pack with a 12v regulator option is for use with the tablet's charging connector which require 12v . A safer option, but leaves me with the charging problem.
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http://www.ebay.com/itm/USB-2-0-fem...ultDomain_0&hash=item3f0cd836f3#ht_2792wt_902
that actually took me a lot longer to find than I had originally planned... lol. of course.... you're going to have to find the rest of your charger. but that'll be easy with that adapter

So its a about making a batt pack which u can connect to the tab via charging port? And use it like a backup when u r out of power?
If its ur idea, you may tell about the size of the pack, and how long u need to use it( ie backup time), if u do, i will find out the solution, also post ur current batt and charger spec.
And hope i can help with some circuits too..
Sent from my HD2 using XDA App

the idea is to have a battery pack that can fit in between the layers of the stand part of this tablet's case. the available space I want to use is about 2"x9" so since the space is limited, the batteries must be the flat type and be able to get 12v out of them and be able to charge them externally.
this is the original tablet battery and the charger is 12v 1.5a.
4x Samsung i9000 1500mAh batteries fits perfectly. and since i already got 2 extra ones laying around, might as well go with these batteries. unless it is possible to get 12v out of 3 batteries. then i can probably use 3 Samsung note 2500mAh batteries instead.
so, what circuitry do i need to make this thing power the tablet and get charged?
thought about getting one of these battery packs, take it apart and replace its batteries with mine. since it already got the necessary circuitry for regulating the voltage and for charging, it would cut down on the guess work and probably be cheaper to build. i think they use 3 batteries in there which would be better.

5 Blinking Lights. Can't figure out what to do here....

Hey, guys and gals.
Well, I found a Nexus 7 in my car the other day and can't figure out who it belongs to. All I know is that I can't boot it up and can't charge it. All I get is 5 blinking white lights. I don't know what it means but I did some research and it seems to mean that the tablet is too dead to boot up. However, it's not accepting any charge even though I charged it overnight. All I am getting is 5 blinking lights now......before I at least got the screen turning on with an empty battery being shown. (If that makes sense)
I am not using the original charger as I don't have one and am instead using my kindle charger. Could that make a difference?
Also, there seems to be some damage around the charging port area...However, the port itself seems to be in adequate condition.
Any ideas?

If it is taking a charge it should warm up a little when it is on the charger.
No warmth == no current going in.
If the battery is so old that it is nearly dead/shorted, the tablet will get HOT when it is on the charger.
So no warmth means no battery connection, either at the USB port or at the battery connector inside the device. There are threads on here from folks who had units where the internal battery connector wasn't seated well and came loose - the teardown to that spot to seat the connector isn't too bad... search for them.
On a 2A charger it takes ~ 3-4 hrs for a 5-100% charge for a N7. That happens initially at about 1500 mA, so it is possible that the voltage on your charger simply collapses if it is only designed for say 500 MA... if that were the case no charging could occur, or only pathologically small amounts of charging could occur.
Also, the N7 has a TI charge controller chip which needs *some* small amount of juice to operate, so it is unfortunately possible for the battery voltage to get so low that the chip can't operate correctly and you get a chicken-and-egg situation where the battery can't charge, even though it is healthy - the voltage just got so low that the charging chip doesn't work. In these cases, an external charger with current limiting is needed to partly charge the tablet battery to get the voltage up high enough so it can be reconnected to the tablet and charged normally. Note that this is a 3rd scenario where you wouldn't feel any "charging warmth" even though all the connections are good.
There is a report on here of someone doing something incredibly stupid - getting some charge onto the tablet battery by disconnecting the battery connector from the tablet and directly connecting it to a car battery to charge it (That's a recipe for a battery explosion or fire). Please don't do something like that.
Something a little less stupid would be using a power resistor (e.g. 5 Watt, 30 ohms) in series with the car battery to prevent too much current from flowing. That would be safe even if the tablet battery was a dead short ( 413 mA, 5.1 Watts in the resistor ), and if the tablet battery was healthy-ish, it would trickle charge at ~ (12.4-3.0)/30 = 313 mA with 3 W dissipated in the resistor.
The important point here is that wall-wart USB chargers are designed to produce 5V up to a certain current level, but they don't actually control the amount of current; that's the job of the funky chicken-and-egg TI charging chip in the N7. So you can't just hook a 5v supply directly to the tablet battery - as you have removed the current limiting control you need something to replace that function: either something dumb to limit the current (such as a power resistor), or a slightly more advanced charger that allows you to limit the current output to a moderate maximum rate.
Note also you don't need to fully charge the battery this way; you just need to bring the charge up a few percent so it can be reconnected to the tablet and charged the "ordinary" way.
good luck

bostonbeast225 said:
Well, I found a Nexus 7 in my car the other day and can't figure out who it belongs to.
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Really? [emoji15][emoji41][emoji56]

bluebirch said:
Really? [emoji15][emoji41][emoji56]
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OP could be a cab or uber driver or something like that

Did u ever get this sorted