Originally Posted by Julia2005
The generator starts off the house batteries. Try connecting a volt meter to the house batteries and try and start the gen. see what voltage the batteries read when trying to start. If the voltage drops below 10 volts your batteries are bad.
I disagree. It's probably a bad / corroded connection between the genny starter and the battery. Might just be a battery ground cable.
A volt meter takes zero current to operate. You could have a corroded / bad connection between the battery and the genny control box or even to the genny starter that passes no current but passes full voltage but has a total loss of voltage when any real current flows.
So start with your volt meter from the battery to the chassis and see full voltage. Punch the genny starter and see full voltage at the battery.
Then move the voltmeter and measure from the genny control box to chassis and then have someone punch the start button. The from the genny starter to chassis and punch the button. When you find point where the voltage drops when your partner hits the genny start button then you've found the problem... Somewhere between the location that had full voltage and the location that had a serious voltage drop is the bad connection. Fix that bad connection so it has full voltage under load and it will work fine. I spent most of a day trying to find the issue on my friends genny and found a corroded ground strap from the genny frame to the RV frame.
It's when you have the voltmeter on the actual battery posts and then hit the starter and the voltage drops to 10 or lower that the battery is bad.
10 volts is a significant number for a 12 volt battery as it is made up of 6 cells of 2 volts per cell. A battery showing 10 volts with nothing connected to it has a cell that is shorted internally.