About 4.2 V reaches the RAM yet the game still forgets its settings.

Battery voltage at the RAM but memory still lost

Cause: The CMOS RAM at 5D has failed.

Checks

• Confirm the battery voltage at the RAM supply pin first.

Fix

• Replace the RAM: a 24-pin 5117 on revision 1 boards, a 28-pin 2064C or 6264 on revision 2 and later. Some early boards use a 24-pin 6116.

Systems

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

Related tips

• CPU still will not boot after the basics
• PIA LED lights, goes out, then lights again
• Replace a failed 6116 RAM with a 6264
• No sound, only amplifier hiss with the volume up
• The CPU memory battery is built into a non-socketed RAM chip
• U15 CPU and U25 RAM substitutes
• Game resets every two seconds
• Resets remain after rectifiers, caps and connectors are done

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