NVRAM or an Altek board.
Worse case, get a three AA battery holder, solder wire to it, add spade lugs at the board, and have the wire long enough for the battery pack to be on the coin box,run the wire to the board. That way you don't have to remove the backglass to replace the battery. Make sure you use male and female lugs so you can't reverse polarity at the MPU. Don't forget the diode so you don't try to charge the AA batteries.