The game reports a low battery or bad U3/U6 memory error a month after the coin cell was replaced, though it has hardly been played.

Low battery error comes back a month after a new coin cell: the new cell was bad

Cause: The new coin cell was faulty and had dropped to about 2.5 V.

Checks

• Measure the coin cell with a meter; a good one reads about 3 V.
• Check new batteries with a meter before fitting them.
• Inspect the board around U3 for heat damage while it is out.

Fix

• Fit a new, good quality coin cell (and do a factory reset if the settings are corrupted).

Systems

• Gottlieb System 3

Games

• Shaq Attaq

Related tips

• Garbage settings and endless balls after a battery change: do a factory reset
• Low battery / Bad U3 or U6 error and beep loop after a coin cell swap
• Gottlieb System 3 CPU passes test ROM, then watchdog trips: torn trace and wrong parts
• Garbled replay score setting after a battery change: repeat the factory reset
• Suddenly won't boot, CPU and DMD LEDs solid, display dark: reseat playfield ground plugs
• Where the boards sit in a System 3 dot matrix backbox
• "Control board error, Low battery or Bad U3 or U6"
• Judging battery corrosion damage

Source: Pinball Repair help group!! (Facebook group)