As long as you keep them as close to a storage charge as possible while not in use any way will work fine.
I don't have a "gauge" so I just charge up a bunch of USB devices with the "leftover" till the battery is almost gone, and then I charge...
But if I just delete the existing fly I think all my waypoint missions will be deleted, which I definitely don't want to do. It's interesting that my current fly version is 1.19. But softonic only has these: I can't find my screenshot. Maybe later.