3.7V rechargeable lithium-ion battery. High capacity replacement batteries for ATAK™ brand (and many other) rechargeable flashlights. No memory effect - recharge up to 1200 times whether fully or partially drained. Built-in circuit protection to ensure proper venting, prevent overcharge or discharge. Capacity: 2600mAh; Voltage: 3.7V; Battery size: 2.62" x 0.72" (69.2 mm x 18.3 mm).