First, scrounge on every source of rechargeable batteries you can get, for instance cellphone batteries from your family’s broken cellphones, broken mp3 players, broken PDAs, any device that needs charging. Also, you can buy cellphone batteries from very old models like the Nokia 3310.
The cellphone also contains excellent DIY stuff that can be hacked like the LCD panels, small motors for vibration, and others for your use! So don’t throw them away first, they’ll be useful for future projects.
Here are the batteries in one place:
Note that the second battery from the left is a PDA battery, and the rest are cellphone batteries.
I’ve soldered the terminals with red (as the positive terminal) and black (as the negative terminal).
Then, assemble the batteries according to your preference. Mine’s like this:
You can use plastic panels to build the casing if you like, but I prefer it to be simple so I used electrical tape, which is quite strong and durable.
As for the recharging, use any extra battery chargers that you have (I had a lot of it!)
Just dissect the charger from its plug, and solder new pins so that it can be plugged into the new battery pack. The basic rule is that the positive terminal of the charger should be connected to the positive terminal of the battery, and so for the negative terminal, while charging.
I always had people from the ‘net warning about the battery might explode if we recharge it ourselves, but I had been doing the things I did with around 20 of them, and none ever did. Just to be safe, you might want to cover it with a protective casing so that IF it does explode, the casing will take the load.
One tip I discovered: A weak battery can be 'recrystallized' by reverse charging it for a few hours to restore some of the battery electrolytes. To be safe, put some protection in case the battery leaks or ruptures when doing so. I take absolutely NO responsibility for any accidents which might happen.
That’s it! A 4.5V rechargeable battery pack costs around RM70 here, but you can build one yourself virtually for free! And what’s even better is that you can customize your battery pack design to fit your prototypes!
Another thing to bear in mind: It is okay to connect different types of batteries in series, because as long as each battery is delivering their own share of power, it should be okay, except if one of the batteries run out of power to be delivered, then you need to recharge it so that it doesn’t reverse-charge itself (a phenomenon inherent to batteries; it reverses its polarity when it runs out of power. Beware that it might explode if ignored) so you need to continually monitor each battery from time to time.
That’s all, see ya soon!
