ARB-L21-5000 is a high-capacity 21700 Li-ion rechargeable battery built for more power and longer runtimes. Additional features include a protection circuit in the anode to help prevent short circuits, over charge/discharge and over heating. Pressure relief vents which expel waste gas in the rare case of an internal short circuit preventing an explosion. Battery capacity up to 5000mAh. 500 charging cycles.Currently compatible with theHT18,LR35R,PD36R,PD40R V2.0,TK22 V2.0,TK22 UE, andTK30. The TK22 V2.0 and TK22UE require a charger to charge the battery. Important Note:THIS BATTERY IS NOT COMPATIBLE WITH 18650 FLASHLIGHTS OR OLDER STYLE CHARGERS. COMPATIBLE CHARGERS ARE THEARE-A2, ARE-A4, ARE-D1 OR ARE-D2.