The pod ;
..located on the underside of the legshield sits roughly level with your knees.
Contains a fragile ULA chip that is a bit temperamental at the best of times but will certainly get fried if you connect your battery the wrong way round
(that's why a c5alive wiring kit is a good thing when discarding the keyswitch assembly, the kit has protection against that happening)
You can bodge a c5 to run without one, but it is useful - part of the protective circuitry that prevents over discharge of your battery and overheating your motor.