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Xbox 360 Controller DIY Rechargeable Battery Pack

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Here at FPX, we hate spending money when we don't have to. So obviously we were pretty irritated to find out that even the latest Xbox 360 controllers don't have built-in rechargeable batteries like the PS3 controller. Since buying a pack of disposable copper tops for around $20 is an idiots solution, we chose to go the rechargeable route. We could have bought one of those Magnetic Induction Chargers made specifically for the xbox, but we didn't feel like making a trip to the shops and the shops were closed anyways. So we made our own significantly unfancy rechargeable battery pack.

Finding a suitable battery

The first step was to raid our pile of old phones. The Xbox 360 controller runs on two AA batteries, or 3 volts. A "dead" AA  gives a voltage of ~1.15v, so the voltage range we want is around 2.6v - 3v. As it turns out, apparently all cell phone batteries are marked as having a 3.6v capacity. That is a bit too much (a full charge is 4.2v), but its certainly not unsafe for the controller.

(Andrew Forgrave / Flickr)
Since all the batteries are essentially the same, its simply a matter of finding the one with the best fit and the best look. The approximate dimensions of the battery compartment are as follows:
 length (to bottom lip)
 bottom lip depth
 interior ridge height
 width (slightly tapered)
 distance between battery posts (center)
Our donor phone wound up being an old sony ericsson from circa 2004. This battery fits like a glove.

Connecting the battery to the controller

Obviously, the connection poles in the controller wont mate up with those of the cell phone battery.We took a dead 9v battery out of a disused stompbox and disassembled it, planning on using strips of the metal case as conductors. However, upon opening the battery, we found a precious gift.
Click to enlarge
Those brown strips of paper contain flat conductors that are the absolute perfect size for this project. With these in hand, it is simply a matter of trimming the conductors to length. As an added bonus, if you have to route the conductors on top of one another, they are already insulated. Score!

The next step: Soldering

This part is pretty simple. It is also really simple to screw up. It is pretty much mandatory that you use flux. Otherwise you run the risk overheating the battery, which will either break it or, in the worst case, cause catastrophic failure. The second important thing you must do is roughen up the battery pads. This can be done with a knife or anything pointy, really.
Note that the ends were trimmed a bit to fit

Finishing up:

You may notice the white stuff in the picture on the left. It is foam tape used for sizing goalie masks. The two layers together are about 6.5mm thick and keep the battery from sliding too far back in the compartment and thus on the connectors in the controller.

Charging the battery

Positive to positve, negative to negative
The best option is to add some wires into the phone and then connect those to the battery when it needs charging. This will prevent overcharging and damage to the battery. Failing that, you can just as easily clip the ends off of any ~5v phone charger and use it directly by connecting the positive lead from the charger to the positive terminal on the battery and the negative lead from the charger to the negative terminal of the battery. That bears repeating so Positive to positive, negative to negative. It takes only about an hour to charge the battery from a dead state(3.0v) to full charge(4.2v).
Read More Charging info at the battery university.

Final thoughts

Like a glove
It gets about 10-15 hours of play time per 60-90 minute charge
. Not bad for a battery thats nearly 10 years old.

Demo video coming soon.