It seems this particular battery chemistry is known to have ignition problems.
Is there a battery technology that is risk-free? You have two risks. Chemicals (or gasses in fault conditions) when the case is compromised (heat, mechanical or pressure-relief valve). Heat, if the charger is over-delivering to a charged battery or if the battery is discharged too fast. One would prefer not to have batteries. It is do-able with fuel cells or micro APUs running, say, on ethanol. I don't mean run the existing APUs off ethanol, but replace the APU's service battery by a fuel cell or baby motor. It's all interesting from a technical pov and speculation, but the time needed to incorporate the technology into a civilian airliner is ten years. Would be faster in wartime. Six months.