Product details:

For use with the liftmaster 3800 jackshaft garage door opener and estate series models 2500, 2500b, 2500d, 3500, 8500 always charged and ready, the ever charge powers the garage door opener to open and close the garage door up to 20 full cycles when the power goes out. Audible signal sounds when door is moving under battery power. Bright led lights let you know that the ever charge is operable, when it is in use or when the batteries need to be replaced. All safety and security features still operate. Simple to install. It sits on top of and plugs right into the back the opener. For low headroom installations, the ever charge can also be mounted to a joist/rafter on the ceiling.