Vintage Synth Repair

Hey,
So Ive got the replacement battery ready to replace it only to find
the guide I was following is for a different model, the battery is
hard to get at(without taking out the key section) is there any way
around this besides taking it all apart besides the main panel, I'm
novice in electronic repair but I would like to do it to not pay the
expensive repair costs, I was thinking maybe i could just solder to
wires to the existing polarities and hook the battery up that way?
would that interfere with anything or could it be done? any tips or
suggestions would be greatly appreciated.

Thanks