What was found
AFTER LEVEL OFF AT FL390, APPROX 20 MIN AFTER TAKEOFF GOT LVL 1 BATT LOW ALERT. DIVERTED TO KLAS BATTERY SHOWED AMBER BOXED. REMOVED AND REPLACED ACFT BATTERIES IAW AMM 24-34-02-4. PERF DC TIE BUSS OPS CHK. REMOVED AND REPLACED BATTERY CHARGER. REMOVED AND REPLACED BATTERY AMMETER SHUNT S4-1 RELAY, BATTERY CHARGER TRANSFER R2-217, RCCB BATTERY CHARGER B1-157, AND REPLACED PLUGS P1-1957, P1-1958, AND P1-1959 PER SWP. PERFORMED WIRING CHECKS PER AWD 24-33-01. PERFORMED EMERGENCY POWER TEST WITH NORMAL FINDINGS. STARTED APU WITH NO FAULTS AND BATTERY RECOVERY NORMAL AFTER START. RAN ALL 3 ENGINES PER JRH AND POWERED ALL 3 BUSSES WITH NORMAL RESULTS D/C SYSTEM CHECKS NORMAL.