Not building a wireless keyboard? Skip ahead to the Microcontroller.
This is an optional step; you only need to do this if you are using a wireless controller.
Fire hazard. It is absolutely vital that you check the battery polarity, even when using a battery that uses a JST jack. The black wire needs to match with the - pad, while the red wire needs to match with the + pad.
Fire Hazard. It is absolutely vital that you do not, in any circumstance, let the exposed wires of the battery touch one another, or otherwise cause a short between the + and - pads. You can use electrical or kapton tape to isolate an exposed wire or pad while soldering.
If you’re socketing your controller, you might want to install the controller first, then remove it from its sockets, install the battery and insert the controller into its sockets again. Ensure there is enough space for the battery before soldering the socket pins, though!
Plugging into a JST jack
Soldering battery leads