This is Ledlenser's own 21700 lithium-ion rechargeable battery, used as a spare or replacement cell for compatible Ledlenser torches and headlamps. It has a capacity of 4600 mAh at a nominal 3.6 V, giving 16.56 Wh of energy, in a steel housing with a PVC wrap. The cell measures about 76 x 22 x 22 mm and weighs around 70 g. Ledlenser lists it as compatible with the P7R, P7R Pro, P7R Signature, TT3R and the H7R Core, Work and Signature headlamps, among other models that use a single 21700 cell. Carrying a charged spare doubles your runtime on long nights, camping trips or shifts, and the cell can also be charged and carried in a Ledlenser Flex power bank. Always check your light's manual to confirm it takes a 21700 cell before buying. Supplied as a single battery.