Isn't it significant that all of these battery failures seem to take place while the aircraft is on the ground. This would seem to suggest that there is something that happens to this battery when the aircraft is not flying that causes problems.
Looks fairly obvious to me. The issue is with charging. Charging happens after the aircraft has been sitting around without a power source for a while, which only happens on ground. So that bit is good news, the chance of an incident is much higher on the ground than in the air.
For that very reason, I would think twice to start the APU in flight, which means discharing the starter battery and re-charge it once the APU is running. So far the issue only happened on ground, where the APU is typically started before the engines are switched off.