Change the CPU backup batteries yearly, with the game on

Replace the three AA cells every year. Do it with the game powered on so the audits and settings are kept. Replace the holder if it shows any corrosion.

Line voltage is present in the backbox with the game on; touch only the batteries.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• Repairing battery corrosion on the CPU board
• Repair battery corrosion on the CPU board
• Replacement battery holder for the CPU board
• Battery orientation on Data East and Sega CPU boards
• Check that battery power reaches the RAM at 5D
• Fit a remote battery holder
• Where the main chips sit near the CPU board batteries
• Other CPU jumpers and what they set

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Three, Clay Harrell (pinrepair.com)