The 18650 Li-Ion Rechargeable Battery from Fenix is the 3.6V, 3400mAh rechargeable equivalent of two CR123A batteries. It is compatible with flashlights and electronics that accept Li-Ion battery chemistry. More than just a battery, it has no battery memory and negligible self-discharge while charged in storage. A built-in pressure relief valve vents gas, preventing them from building up in the battery. Integrated safety circuitry helps prevent over-heating, over-charging and over-discharge. The housing has dual-layer design at the positive end that gives it impact-resistance.