As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AUX BATTERY DID NOT SHOW NEGATIVE VALUE WITH BATTERY SWITCH ON AND GRD PWR SWITCH OFF. GROUNDED - YES. PERFORMED FIM 24-31 TASK 801 NO FAULTS. REMOVED AND REPLACED MAIN AND AUX BATTERY NO HELP. REINSTALLED ORIGINAL MAIN AND AUX BATTERY. PERFORMED OPS CHECK OPS CHECK NORMAL. AUX BATTERY SHOWED NEGATIVE VALUE WITH BATTERY SWITCH ON AND GRD PWR SWITCH OFF REF AMM 24-31-11.