Hi,
I suspect the batteries have nearly never been fully charged. It can take up to 168 hours.
There are heaters that use no power and do vent exhaust gasses out side. They are not cheap.
There is a unit called a
Platinum Cat which is vented. These do have a thermostat and being vented also prevent moisture build up inside the RV. This is the only catalytic heater I'd feel safe to use while sleeping.
I would never use a blue flame heater while sleeping. Your rv comes with at least three built right in. I.E. the stove top.
Since there is no room for more battery capacity, if you have deep (and I do mean deep) pockets you could shift to LI batteries.
If LI is going to break the bank, then go solar with two brand spanking new batteries. 150 watts of solar per 100 amp-hours of battery bank.
Replace all the incandescent lighting with led technology to conserve power.
I chose to "give up" a compartment to more than double the battery capacity.
