The batteries I am using here are Canon BP-915 or Canon BP-911 camcorder batteries as I use them in my projects for making handheld portable video game console systems. The principles and methods are however similar for other makes, brands and sizes of cells.
Li-ion batteries, like ones from camcorders, are made up in multiples of 3.7v cells, so for a 7.2v or 7.4v battery pack, you actually have two cells inside, for 11.2v you get three cells inside.
As long as you are careful, it is quite easy to segregate the cells and rewire the batteries, keeping the battery protection circuit in place, to stop over and under charging. Also in this guide, I cover how to connect the battery terminals to a charging jack.
Step 1: Release Tabs
Step 2: Pry the Casing Off!
If the case refuses to come off without a fight, use pliers to hold the metal tabs and lift up the plastic casing, to separate the two case halves. Holding the metal tab in place takes the pressure off the circuit board.
Step 3: The Protection Circuit and Wiring the Battery Pack
They come designed to work for a given amount of cells and also voltages, so don't replace them with other similar circuits as if they are wrong, you could have an explosion ready to happen. This is a great advantage in using Li-ion cells, they have the protection circuit built in.
Also, it is important to use a battery charger designed for the brand and type of batteries you are using.
Regards wiring the batteries - simply extend the wires and contacts in the battery with wires, designed for 3 amps is fine, to the same terminations as were on the battery originally. That will then allow you to separate the cells from each other, and making them easier to mount into your project.
You can't just solder a connection to a battery terminal, solder doesn't stick. Dab on some flux first, then solder from a hot soldering iron, and you should end up with a strong solder blob on the battery you can solder onto. Don't be long with the soldering iron, it isn't good to keep a hot soldering iron against a battery for more than a couple of seconds at a time.
Step 4: Result
The colour of the cells are not important, I have seen orange and red ones, I am sure there are others about too!
Step 5: Add Charging Jacks
In regards to the PSone charging jacks, the middle connection is positive, the two outer are negative.
It doesn't matter what colour wires you use, but ensure positive goes to positive and negative to negative.
On the female port (yellow in picture), wire the "+" to the positive battery terminal, and "-" to negative. Wire the male port (green in picture) the same way, and to the battery charger unit.
In this way, you can recharge the batteries as you need to.
Step 6: PDF and Video for Project
Please visit my Wordpress site for details of more projects!