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. . Important Note: THIS BATTERY IS NOT COMPATIBLE WITH 18650 FLASHLIGHTS OR OLDER STYLE CHARGERS. COMPATIBLE CHARGERS ARE THE ARE-A2, ARE-A4, ARE-D1 OR ARE-D2.