Well of course someone knows, but I AIN'T talkin'!!!
OK, OK, I'll talk.
It uses 2 transponders in the key to start the car. If it's not working to start, something happened to one or both of the transponders. If you have access and want to explore or experiment, hey, it's HIS key, go ahead and try, nothing to lose. I can help explain how to disassemble it if you need help that way.
One of the transponders is a fixed code, one is a rolling code.
The transponders operate without any battery power at all, the batteries are for remote lock/unlock only, and also for the convenience features (rolling up and down of windows and sunroof, which is an IR function (red lense).
Do any of these features work?
DO NOT buy a key from EBay, or a junkyard or anything else but a new dealer key. Smartkeys are vehicle-specific, you can't "train" a key to work on an incorrect vehicle.