The Harbor Freight one has the photovoltaic panels so maybe that keeps it charged? I havn't had a problem with the battery.

Someone asked what I have it set on, I hadn't adjusted it and it came set between 10 and 11, which has been fine with my mig sp-175

'51 Chevy 1/2 ton w/'62 261, HEI, offy, fentons, dual carter/webbers, t-5 & 12 bolt posi