The Enviro-Gen^® is an electrochemical or metal-air fuel cell. The fuel is a sacrificial magnesium anode. The Enviro-Gen^® generates its own electricity once the seawater is added and a load is placed on the unit. if there is nothing plugged in and operating, there is no voltage produced and no depletion, so this is not a `one-time shot`. You can use the Enviro-Gen for several hours, then dump out the water and rinse the magnesium anodes in fresh water and put it back on the shelf. The Enviro-Gen also has an indefinite shelf life and, unlike batteries, is unaffected by hot weather or engine room conditions making it perfect for boaters. The duration of operation is dependent upon the electrical load placed upon the unit. With a minimal load a set of anodes will last up to 150+ hours, with the unit rated at 40AmpereHours. A 5 Amp sump pump, for instance, could deplete the anodes in 8 hours if running full time. The units may also be run in series.