i have 2 earth x installed , each independant of the other. battery #2 is the oldest. right now i start engine on #2 and use it to fly. at sometime in the operation,when taxiing taxi, i switch to #1 to keep it at full charge. my logic is that i am using the oldest battery first in flight and if a battery fails in flight my backup battery is most likely the healthiest of the 2 batteries. is my logic sound? any other opinions please let me know.