The Sightmark 2-pack of Rechargeable Lithium-Ion 18650 Batteries replaces those that come with Sightmark's H2000 and SS2000 flashlights. These batteries fit the chargers that are packaged with the lights and can recharge in 3 to 5 hours. They operate at 3.7V and feature a capacity of 4000mAh. They have a shelf life of 2 years. Additionally, they work in any device that runs on 18650 batteries.