It sounds like no one is keeping any type of record to pinpoint the problem. There should be a pattern. Battery Banks are becoming more common and could be the culprit. Batteries almost always charge properly because a wall charge is slow. Backup banks are a relatively faster method of charging. If the BMS inside fails to work properly, then the safety factor is gone. Fixing the problem could be as simple as requiring all passengers to have their stored devices and Banks off or discounted while onboard. Second, have more wall charging accessibility at the waiting area in the terminal so passenger won’t feel the need to recharge in the air.