Revolutionary and powerfully upgraded As a patent product developed by NITECORE the 21700 I series battery is a proprietary 21700 rechargeable Li-ion battery featuring dual way output with positive and negative polarities at both ends and a high energy density. It enables a highly efficient output by minimizing the loss of power due to internal resistance. Unprecedented Battery Performance The dual polarities of the 21700 I series battery at both ends have broken the convention of linking the head and the tail of the flashlight in order to minimize its size and weight. The internal resistance is therefore greatly reduced to offering a direct energy conversion to power the device Safety Features Microporous barrier protects delicate internal components, coated with durable metallic film to guard against abrasion Mercury free, lead free and cadmium free, low cost and environmentally friendly Can be recharged over 500 times. Specifications • Capacity: 5,300mAh • Voltage: 3.6V • Continuous Discharge Current: 20A MAX • Length: 77.2±0.3mm / 3.04"±0.01" • Diameter: 22.2±0.3mm / 0.87"±0.01"