Oh! Ok, I never seen you say it was low, but I see where you were going to check it.
If, after installing new battery, you cannot get to a 61-1 (by pressing white self-test button), then before a new MPU, I would definitely try a Clear. If you have a bill validator, go ahead and order a Set chip, as you will need that as well after the Clear. If that does not work, it sounds like you will be in the market for an MPU board.