Don't worry about the battery. Someone already stuck a NVRAM in your game. That is the black rectangular thing with 5101 on it in your last picture.
If your game is working. I wouldn't worry about ground mods. You may not need them. They may have been done. And you could do more harm than good, until your skill set improves.
NVRAM replaces the battery. This explains it : http://lockwhenlit.com/anyPin.htm
LTG : )