You need to solder a helper battery first.
You must install it with wires in a way it doesn't obstruct the removal of the old battery. Ground is easy to find and the 3.3V line can be found immediately left where the OG battery leg is soldered.
Then you can pull the old battery and solder a new one.
- Sega Super Scaler hardware (Out Run, Model X, Model Y), not working (even with faulty PCM chip)