ARB-L21-4000P is a high-capacity 21700 Li-ion rechargeable battery built for longer runtimes at higher levels. This battery allows a high-output flashlight like the LR35R to have its turbo setting of 10000 lumens to maintain its output by maintaining higher voltage for longer periods of a battery's charge. Additional features include a protection circuit in the anode to help prevent short circuits, overcharge/discharge, and overheating. Pressure relief vents expel waste gas in the rare case of an internal short circuit preventing an explosion. Battery capacity up to 4000mAh. 500 charging cycles. 21700 battery type 4000mAh high capacity Protection circuitry to prevent short circuits Pressure vents to prevent explosions 500 charge cycles Currently compatible with the HT18, LR35R, PD36R, PD40R V2.0, TK22 V2.0, TK22 UE, and TK30. Capacity: 4000mAh Voltage: 3.6V Charging Current: Recommended 1A, maximum 4A Maximum output current: 18A (less than 3 minutes) Maximum continuous output current: 10A Weight: 2.5 ounces (70g) Size: Length: 2.99? (76mm) Diameter: 0.85? (21.5mm)