The Fenix 21700 battery can handle twice the power of a standard 18650 battery.
The additional mAh's allow flashlights like the PD36R and TK22 to have longer run times.
What makes this 21700 battery even better is the USB Type-C charging port that is embedded in the cell. You don't have to use a separate charger to charge the battery; it can all be done with a wall adapter and USB Type-C charging cord similar to that used for many mobile phones.
