The Fenix ARB-L18-3400 is a high capacity 18650 Li-ion rechargeable with a protection circuit in the anode to help prevent short circuits, over charge/discharge and over heating. The battery also includes pressure relief vents which expel waste gas in the rare case of an internal short circuit preventing an explosion.

Specifications and Features
ARB-L18-3400 Rechargeable Battery
3400mAh high capacity
Protection circuitry to prevent short circuits
Pressure vents to prevent explosions
500 charge cycles
Voltage: 3.6V