Putting battery packs in parallel to increase capacity. How to do it?

[GothicIII]

Hello,
I thought this is a topic that fits best here.
Having multiple Li-Ion, Li-Po batteries lying around and devices were the battery started to die...
Is it possible to wire batteries (ofc only same chemical types) together and make it a huge battery pack?

Would be extremely beneficial for small devices like the PSVita, were you can cramp multiple small battery packs together instead of a huge one were you'd need to sand down the inner housing to fit it in.
Also I have a keyboard which has like a 3.7V 10000mAh lipo battery and there is no replacement I can get easily in my country. The best I can buy is 3000mAh and that would mean I'll better use a cable permanently.
There are also batteries with 3pins and 2pins. Latter are obviously + and - but what does the 3rd pin do? Battery information? How to wire that in parallel?

I am also aware of the problem of batteries not beeing equally charged. How to even them out?

Is there a guide/site out there which explains the cons and solutions? Or is it too complex and this is a waste of time?

 

[master801]

The third pin is usually the data line (for the device to communicate with the battery's chip.)

 

[Ryccardo]

what does the 3rd pin do? Battery information?

Usually it's a thermometer (NTC), unlikely to be data but it's possible (see the PSP, in which case you keep the original electronics as-is or better yet reprogram them with the new values)

I am also aware of the problem of batteries not beeing equally charged. How to even them out?

The first time, you charge them separately then use a balancer;
while assembling the pack, you should use a BMS, that connects in series with the battery as a whole with respect to the device (and at various intermediate points of the pack) that handles it...
Poor man's alternative being using only protected cells, connecting them directly in parallel (after the initial balancing) and relying on the voltage and current limiting of each element, can't say it's a good design but lots of chinesium spycams and mp3 players with a diode as the only charging "control" rely on this...

 

[GothicIII]

Usually it's a thermometer (NTC), unlikely to be data but it's possible (see the PSP, in which case you keep the original electronics as-is or better yet reprogram them with the new values)


The first time, you charge them separately then use a balancer;
while assembling the pack, you should use a BMS, that connects in series with the battery as a whole with respect to the device (and at various intermediate points of the pack) that handles it...
Poor man's alternative being using only protected cells, connecting them directly in parallel (after the initial balancing) and relying on the voltage and current limiting of each element, can't say it's a good design but lots of chinesium spycams and mp3 players with a diode as the only charging "control" rely on this...

Do you have any more details on how to do it properly? Based on your description I only could do the poor man version. :/

 

[FAST6191]

There is the second option and reasonably achievable otherwise. That being have the three batteries mounted however you will but have a switch that selects between them -- basic multi throw single pole may do it, might do two poles if the third pin needs to be present in which case dp3t might be a choice thing to search for). You would want to power down between switching, or maybe see about getting a capacitor of enough capacitance (though risks some issues with charging, not to mention charging would have to be done on a per battery basis unless you want to get a bit more creative with an external setup) such that it powers it during the switch.

I don't know what the situation in the gambia is like if that is where you are buying; a guy I know used to go a lot and it gets tricky/the sorts of things he would bring would attest to it maybe not being a trip down the real world shops or casual online here the next day like it might be here. On the flip side there is a reason I do his electronics.