The T.M.P.R. SYSTEM is a modular system of purpose-specific optics that can be used individually or in combination to create the ultimate sight for any situation. Each T.M.P.R. System component has its own battery. When connected to a T.M.P.R. prism sight, they can be powered by the prism sights high-capacity CR123 battery. Automatic brightness sensor adjusts brightness to match the environmental conditions; has 3 manual brightness settings. Battery access is conveniently located on the top of the sight; automatic time-out feature after 8 hours helps battery last up to 5 years.