Super Mario RPG: Legend of the Seven Stars (Super Nintendo, 1996)

To make a long story short..a friend of mine who's fallen on bad times gives me this game to sell for him and I can't get it to work..
I've cleaned the contacts something I know very well how to do but no matter what it won't start,I just get a Black Screen,and no audio..

I know the question on how to repair these games probably has been asked here a thousand times..(feel free to link me to a thread)..But I'm not having any luck finding info nor on youtube.
Youtube actually has posts with people having the same issue with this very game but the answer always is clean the games contacts or a lead to sell the person a cleaning kit=UGH!!..

This game has a battery,I've yet to check it for voltage..Before I change it I'd like to know first if a dead battery would cause the game not to work or is this game just dead..?

This is not the only game I have that's dead,I also have a SNES Mario All Stars/Super Mario World cart..it also won't start,black screen..

Thank you for any help..