Sorry - the cables don't go to the starter. I have chassis batteries for that. I believe they go to the inverter - a Xantrex 458 Freedom.
Here's a picture of the batteries cleaned up. I did check the back 2 batteries with a hydrometer and they are good to go.

When I say that the batteries are discharging rapidly, I say this based on the reading on the remote panel connected to my inverter. When I initally got the RV I could get quite a bit of use of the RV with the inverter turned on before the batteries discharged. The kids could watch TV for example. I currently get very little - if I disconnect from ac with batteries fully charged I get very little battery life. The batteries go from 12.5 volts down to 10.5-11 volts per the remote panel on my inverter quickly.