Opening Up and Modding a Li-ion Battery and Connecting Into a Gadget to Recharge As Needed

Why is this useful? When you're making an electronics project, like a portable handheld video game console system, it isn't easy to house a large battery pack inside the enclosure; however if the battery is able to be split into two parts, it means it is far easier to locate the batteries into your project. My hobby is making handheld portable video game consoles from consoles not designed to be used as such; so using good quality batteries are important to my work, and locating them in a case so they fit ok is important.

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.

Here's how... 

There are two metal tabs on the sides of the battery, one is for the positive battery terminal and one for the negative battery terminal. Get a pair of pliers to snap off the plastic surrounding the tabs, and then with a small screwdriver, pry the metal tabs free. 

 Insert a fairly large screwdriver with a narrow edge into the groove between the two case halves to pry them apart. Don't force the screwdriver inside or you may damage the cells if being too harsh. Also, don't use the screwdriver anywhere near where the voltage tabs are, as between them is a small circuit board you must not damage (the battery protection circuit).

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.

The protection circuit (the green board in the picture) is vital - it stops the batteries from draining too much (which would cause the batteries to swell, and get damaged, maybe explode if subsequently recharged), or over charging (batteries would literally explode like a small granade). It is therefore important not to damage the circuits.

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.

This is an example of where it is useful to separate batteries. 

The colour of the cells are not important, I have seen orange and red ones, I am sure there are others about too!

If the batteries are dismantled, you can't plug them into the charger anymore, so it makes sense to add a female port charger to your gadget, and a male one to the charger unit. The charging jacks are taken from a PSone console / screen, although of course you can use a male and female port from whatever suitable you have.

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.

Here is a PDF file from my Wordpress site on this subject, along with a video too, showing the steps in more detail.

Please visit my Wordpress site for details of more projects!

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