I am lost. Please help. I have a 2021 trailer. Suburban SF 20 furnace. The furnace works great on shore power, batteries still online. But when on battery power only, furnace will initially come on. Heat to set temp, but once there. It shuts off. Temp drops, evacuation fan comes on, but furnace will not fire, and everything shuts down. I go to thermostat, shut off, wait a till it clicks off. Then reset to heat, it comes on again and works fine, until temp reached, then it will not start until I cycle thermostat. Plug in shore power. All is well again. I started with 12 rv battery. Added a second thinking power problem. Still did it. Replaced them with 2 glass batteries. No change. Added solar panels. No change. Replaced converter. Replaced circuit board. Still doing it. I am at wits end. Batteries are always showing 12.6 or better. HELP.