With a fresh battery fitted and the game power-cycled twice, the low battery message still appears.

Battery error stays after a new battery

Cause: The DS1210 battery controller at U6 is faulty.

Checks

• Confirm about 3.2 V at U6 pin 2 against pin 4.

Fix

• Replace U6 (DS1210).

Systems

• Gottlieb System 3

Related tips

• Logic chips worth stocking
• "Control board error, Low battery or Bad U3 or U6"
• Battery reads 3 V but the game says it's low
• Using a remote two-AA battery pack
• CPU battery and socket parts
• Constant beeping, display blank, GI on
• Lithium battery leak damaging the CPU board
• Nonsense message at boot, game stuck in a loop

Source: Repairing Gottlieb System 3 Electronic Pinball Games from 1989 to 1996, Clay Harrell (pinrepair.com)