I think it's 600 watts...the 2 six volt batteries are wired in series, not parallel to provide 12 volts, the only reason for that was space (MGB's had the same goofy thing). So, depending on the output of your altenator/generator(regulator) and battery capacity you should, on a rated 50 amp 12 volt battery equivelant would be 12X50 which would be, of course 600 watts.....