What was found
BATTERY DISCHARGE LIGHT ILLUMINATED DURING CLIMB THROUGH APPROX FL 220. MAIN BATTERY SHOWED -5 AMPS DISCHARGE RATE. AUX BATTERY SHOWED POSITIVE CHARGE RATE. LIGHT EXTINGUISHED AFTER APPROX 8 MINUTES OR SO BUT MAIN BATTERY CONTINUED TO SHOW -2 AMPS. MAIN BATTERY CHARGE RATE RETURNED TO NORMAL DURING DESCENT. GROUNDED - YES. DIVERSION TIME 36 MINUTES. REMOVED AND REPLACED NR 1 MAIN AIRCRAFT BATTERY CHARGER REF AMM 24-31-21 GROUND VERIFICATION CHECKS NORMAL.