A genuine Ledlenser 18650 lithium-ion rechargeable battery with a capacity of 3000 mAh (Ledlenser article 501001). The 18650 is the standard cell used in many mid-size Ledlenser torches and headlamps, and a spare lets you swap in a charged cell and keep your light running on long jobs or trips. The cell has a steel housing with a PVC wrap and weighs about 47 g. It is designed for lights made for a single 18650 Li-Ion cell; always confirm in your light's manual that it takes an 18650 before buying, and charge it in the light or a suitable Li-Ion charger.