Battery

To keep the chassis battery charged I would recommend the BIRD a Bi-Directional Isolator Relay Delay

It charges both batteries when either one is
being charged. When the coach is being driven,both
batteries will be charged from the engine's
alternator. When the coach is plugged into shore
power,both batteries will be charged from the
converter. If neither battery is being charged, the
batteries are fully isolated. The controller also
senses heavy loads on either battery to prevent
the wrong battery from being inadvertently
discharged.

While sitting even while plugged in, if some type of charger is not hooked up to the Chassis battery it will go dead from the parasitic loads.

I keep mine plugged in all the time at home and with the BIRD both Chassis and House batteries stay charged.

8.3 volts? I assume they are shot.

Charge overnight and see what they are at. Then let them sit disconnected for another day or two and see if they hold 12.6+ volts.

Ok I got the old batteries out of RV.They are worldwide 24DC-4 deep cycle batteries.I also bought Noco genius 35000 smart charger and a auto craft hydrometer.First I checked the voltage of two separately and it was 8.3 volt by voltmeter.Than I checked the SG with hydrometer and it was 1.10 in all 6 cells of one battery and 1.2 in all 6 cells of other battery.1.1 in red zone needing charge and 1.2 in fair range on hydrometer.Now I connected the ist battery to the charger for charging.It show 25 percent or below charge status.According to charger user guide now I have to wait at least 14.3 hours for full charge.Now with above info do you think these batteries are salvageable or they are shot.I have an option of repair in the new charger I bought which I can use.

I got my GC2 at Costco. I recommend a converter upgrade to maintain the batteries. If your house system does not charge the chassis battery I recommend the Trik-L-Start combiner. Post your current converter model for best suggestions.

We get our 6 volt GC2 batteries from Samsclub, first set we purchased at $60 each a decade ago were Interstates and still had life in them going on their 8th year, we traded them in for our current set of Duracells at $80 a piece, they have provided 3 years of service thus far. We do most of our RVing off the power grid and our batteries are worked pretty hard, we use solar and generator to get them back up and ready for another day of heavy demand.

We have an Iota IQ4 converter on our rig and it does a good job of keeping our batteries happy and healthy, we keep our rig plugged in 24/7 when stored in our side yard. I buy them from Samsclub as they have the lowest prices in our area, I would buy the more expensive higher-end batteries but don't see a reason with the longevity we've experienced. Proper charging and routine maintenance is the key, most batteries are produced by a couple of MFGRs anyway.