Specifications: Emitter: SST40 LED Working Voltage: 2.7V - 4.2V Battery Options: 1 X 18650 Li-ion battery Dimension: 101.5mm (length) × 24.7mm (head diameter) Weight: 55g (without battery) Flashlight body: Aerospace grade 6061 grade aluminum alloy USB Type-C Charging Mode Memory: memorizes the last brightness level used in the general modes (except Moon, Turbo and Strobe) Advanced Temperature Regulation (ATR) technology: ATR will adjust the brightness level automatically when the driver temperature reaches a relatively high temperature to prevent overheating. Reverse polarity protection: it cuts off the power while the battery inserted improperly. LVP: while on, if the battery voltage is lower than 2.7V, it turns off automatically. HVP: while on, if the battery voltage is higher than 4.35V, it turns off automatically.