The batteries take quite a pounding though, and fail quickly.
Care needs to be taked as there is a huge amount of hydrogen produced.
Gell cells do not survive long in this application. Kromrey Converters will run self powered for far longer than can be easily explained, but it's quite difficult to rule out shock excitation of the battery electrolyte. The quick depletion of the battery might support this hypothisis. Due to the high frequancy components accross the battery while in operation, measurments are difficult, and the power factor is unsteady, making it quite hard to analize the exact performance of the system. Over unity operation may be present, but is hard to prove.