There are two CMOS chips in your machine. One is on the small motherboard (fixed in the machine) and the other is the removeable MPU board that slides into the motherboard. These two chips need to be in sync - its part of the gaming safety and security protocol.
The CMOS is protected by the battery on the motherboard.
If you were to kill the power right in the middle of a spin - between these two chips the slot would figure out exactly where it left off. complete the spin, payout or any other function that might be underway when it was interrupted. If you were to somehow get access to the guts and corrupt the machine it would go into a failure because these two chips are out of sync.
So when you get a bad battery error 12. The CMOS can get corrupted. It depends on how low the battery goes and how long its been in that state.
The conventional method is to use a CLEAR chip. Then you will need a SET chip to re-activate your bill validator.
There are two different series of GameChips. A 1271 is a newer game chip than a 731. There were considerable changes to the architecture between those two chips mainly to add more accounting items in the newer chip. When you switch between the two you get a 63 CMOS error. You go though the process of turning the JP reset and pressing the white button and the CMOS reformats to the correct format for the chip that is in the system. This has been known to get you around the stuck 61 error some of the time.
If you have to go our and order your self a 731 - I would be ordering a Clear and a Set chip. Your delivery/wait time is going to be the same and the clear chip is the accepted fix.