I agree with NVram,but in case you want to stick with batteries, since you're soldering anyway, extend the wires and battery holder to where you can access it though the coin door instead of removing the back glass. Add enough wire to pull the battery holder outside of the machine so you can see what you're doing.
Make sure you have a way to remove the mother board without removing the battery pack. I use male and female connectors near the MPU to remove it without pulling the battery pack out