One Energizer 123 lithium battery (CR123A size). This 3 V cylindrical lithium cell is used in high-drain devices: tactical and LED torches, weapon lights and red-dot sights, film and digital cameras, flash units, home security sensors and some trail cameras. Lithium cells keep their power well in cold weather and have a long storage life; the pack states 10 years. The CR123A measures about 17 mm in diameter and 34.5 mm long and replaces cells marked CR123, DL123A or EL123AP. It is not rechargeable; do not try to charge it. Recycle used lithium batteries at a drop-off point rather than in household waste.