Can I leave a fully charged lithium-ion battery in an unplugged Fenix charger?
Storing a fully charged lithium-ion battery in an unplugged Fenix charger shouldn't be any problem; however, it's probably not the best practice. These batteries are very powerful and do require careful handling. It is recommended that you put them in a storage device that protects interference to the + and - sides. You surely DON'T want multiple batteries to make contact + to - when not in a device. Another reason not to leave it in the charger is the constant pressure of the springs holding the battery in place could weaken the springs and just not good for the battery.