The Encore emergency battery pack is designed to fit inside most linear fluoresent fixtures or onto recessed downlight frame kits. In the event of an AC power failure, the emergency pack automatically switches to emergency mode powering fixtures for a minimum of 90 minutes. Fully discharged battery will recharge completely in less than 24 hours. Ballasts are compatible with nearly all AC ballast types including standard, rapid start, slimline, instant start, energy saving, dimming and electronic types. Number of lamps in emergency mode - one 2-8 ft.