Electronic – solder 4 AA batteries together in series and make the own rechargeable battery pack


I've bought my young son a couple of remote control tanks for Christmas. They are supplied with two rechargeable 'battery packs' (4 x AA batteries heat shrunk together). The battery pack supplied is Ni-Cd 400mAh 4.8V

The charger says "Output 4.8VDC 250mA".

The reviews of these tanks say they are great but the batteries don't last very long.

I wondered if I could buy 4 x 2850mAH AA batteries and then solder them together to replicate the supplied battery pack and then charge them with the supplied charger and use these instead of the supplied ones?

I've been reading on the internet how to solder the batteries (i.e. don't apply heat for long and 'rough' the ends up first to help the solder stick). But I also read somewhere about 'balancing' the batteries so that they would charge??

The supplied batteries are just linked together (i.e. nothing in there that I could see that would 'balance' them) so thought I would get expert advice on the best way to proceed with this?

I'm fine at soldering but don't want to make a home-made battery pack and then have it blow up when I try and charge it!

I bought a plastic 4xAA battery holder that links the batteries together but it doesn't fit in the tank compartment so that won't work.

Help appreciated 🙂

Best Answer

Edit: see also Is soldering wires directly on a NiMh battery safe?

nothing in there that I could see that would 'balance' them

This may be why they don't last very long.

Due to manufacturing variance, one of the batteries will go flat first while the others have more charge. This can result in current being driven through it by the others while it's flat, damaging the battery. Or the reverse happens while charging: one will fill up first, and then suffer overcharge damage. Does the charger automatically stop on full charge or it it timed?

It may be better to adapt the battery holder to the batteries with a saw, so you can use the holder and charge them individually.

Or look for cheap repurposeable packs, eg. http://www.dx.com/p/gd-509-2-4v-1200mah-rechargeable-2-x-aa-cordless-phone-replacement-battery-pack-white-292547#.VIXLYsmfjjU is clearly 2x AA heatshrunk together, you may be able to find 4 heatshrunk together in the right format then just change the connector.

Edit 2: by the way, I would put money on the tanks suffering mechanical failure or enemy action before the battery packs become an issue. Unless they're expensive 'models' rather than 'toys'.

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