Okay, I will clarify for you – the generator part of the gen set does not have an alternator, the engine part of the gen set does. And, I don't know if, when you don't have a separate starting battery for the generator if it (the alternator on the engine) puts a charge back into your battery bank. I have never turned my convertor off when the generator was running to see if the batteries started losing voltage. However, if as you suggest,the alternator is bad, then the convertor would also have be bad if the batteries were losing their charge in the case as stated and the batteries are in good shape and able to take and hold a charge.