Get the new Berkey Battery Adapter case for your Berkey Light LED system. Complete with on-off switch, the adapter provides backup power for your Berkey LED system. Using the Berkey Battery Adapter case, the low energy LEDs will provide light, 8 hours per night, for approximately two weeks on a single set of four AA alkaline batteries. Thats right, incredibly you get two weeks worth of emergency light for the price of one set of small AA batteries.