AN MD-11 IN CRUISE AT FL290 OVER WATER 700 MILES FROM IT'S DEST ARPT HAS BATTERY CHARGE ALERT FOLLOWED BY BATTERY DISCHARGING ALERT. BATTERY RAPIDLY DISCHARGED TO 6 VOLTS.

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BATTERY CHARGING ALERT FOLLOWED BY A BATTERY DISCHARGING ALERT FOLLOWED BY BOTH ALERTS EXTINGUISHING; AND BATTERY LOW ALERT DISPLAYED. BATTERY VOLTAGE RAPIDLY DECREASED THROUGHOUT EVENTS TO SIX VOLTS. WE LANDED WITH FIVE VOLTS. CREW FOLLOWED FLT MAN PROCS AND CONTACTED COMPANY DISPATCH FOR DIVERSION TO NEAREST SUITABLE ARPT. ZZZZ WAS CHOSEN BY CREW. DISPATCH AGREED. DISPATCH ALERTED ATC AS DID THE CREW FOR THE DIVERSION. FLT MAN 3 WAS THEN NOTED FOR LNDG AT A SUITABLE ARPT. COMPANY THEN RADIOED THAT THE ZZZZ LNDG WAS NOT REQUIRED AND THE CAPT ACCEPTED THEIR REASONING BASED UPON CONVERSATION WITH AND RESEARCH OF MAINT CTLR. OVERFLEW ZZZZ AND LANDED AT ZZZ1. BATTERIES AND CHARGER FOUND WARM. CASINGS WET. CONFLICTING MAINT MANUALS; AND FLT MANUALS. THERMAL RUNAWAY PROCEDURES NEED CLARIFICATION AND IMMEDIATE ATTENTION. FLEW 2 TO 2.5 HRS WITH DEAD BATTERY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE FIRST ALERT HE RECEIVED WAS MAIN SHIPS BATTERY CHARGING ALERT FOLLOWED BY A BATTERY DISCHARGING ALERT THEN FOLLOWED BY BOTH ALERTS EXTINGUISHING AND FINALLY BATTERY LOW ALERT DISPLAYED. THE RPTR SAID THE BATTERY RAPIDLY DROPPED TO SIX VOLTS. THE RPTR STATED DISPATCH AND MAINT WERE ADVISED OF THE BATTERY SIT AND THE MAINT MANUAL AND FLT MANUALS WERE CONSULTED. THE RPTR SAID ONE MANUAL STATED TO LAND AT A 'SUITABLE ARPT'; AND THE OTHER MANUAL STATED TO LAND AT THE 'MOST SUITABLE ARPT.' THE RPTR STATED THE FLT CONTINUED TO ITS SCHEDULED DEST ARPT THE 'MOST SUITABLE ARPT.' THE RPTR SAID THE BATTERY INDICATED 5 VOLTS ON LNDG. THE RPTR SAID THE BATTERY CHARGER AND BATTERY WERE REPLACED.