The Fenix ARB-L16-800UP Built-in USB-C Rechargeable Battery is a 16340 Li-ion battery with a protection circuit in the anode to help prevent short circuits, overcharge/discharge and overheating. This battery has its own USB Type-C charging port for quick/easy charging without the need for a separate charger. The battery also includes multiple levels of protection including overcharge protection, overheat protection, and pressure relief vents which expel waste gas in the rare case of an internal short circuit preventing an explosion.
It is designed to work with: PD25R, LD15R, E18R V2.0, and HM50R V2.0. A USB Type-C charging cord is NOT included.
I've used these in multiple products. Streamlight tlrhl, eotech optics and I have to say. By far the best rechargeable batteries I've used thus far. Planning on picking up a few more soon.