Battery disconnect switch
Most of the more recent motorhomes have a battery disconnect switch. There are usually two, one for the chassis battery and one for the house/coach batteries. When in “use”, 12 volt DC current is flowing from the battery to the RV. When in “store”, the red light goes out and the flow of electricity from the battery is shut off, just as if you had disconnected the cables from the battery(ies).
The chassis battery is charged only by the alternator when the engine is running (the coach batteries are also charged by the alternator). Most coaches have a greater or lesser amount of parasitic drain. Such things as dashboard electric clock, compass, engine computer, steps, etc will all drain a small amount of battery power, which goes unrecognized, until the battery is dead.
Many motorhomes have another switch on the dash which connects the house/coach batteries and the chassis battery together. So if your chassis battery has been drained and wont start the engine, pressing and holding this switch will allow you to start the engine with the coach batteries.
But I believe in prevention of the parasitic drain by “disconnecting” the chassis battery (putting it in “store”) when parked. Besides, the steps will stay down. This is especially important if boondocking and you want the engine to start when you are ready to go.
The coach/house batteries are a bit more complex. If you disconnect the coach batteries by putting them in the “store” position (red light goes out), and then plug in to the power post (red light comes back on, but batteries are still disconnected), part of the 120 volt AC current will go to the 120 volt electrical appliances and outlet plugs, part of it will go through the converter and be converted to 12 volt DC to run all the 12 volt appliances (furnace fan, vent fans, lights, refrigerator, igniters for range and water heater, etc). I have subsequently learned that for brands other than Rexhall, the 12 volt appliances may or may not function when the battery disconnect switch is disconnected.
If the battery disconnect switch were left in the use position, and you plugged into 120 volt power source, then a portion of the 12 volt DC electricity coming out of the converter would go to the 12 volt appliances, and part of it would go to the coach batteries, and charge them.
For economic reasons, most moderately priced RVs have a single stage converter which is slower to charge the house batteries than a 3 stage, does not have a trickle charge, and often will overcharge the house batteries. So if you are not disconnected, the red light will stay on once you plug in, the batteries will continue to be charged for as long as you are parked, and battery life will be shortened. Rexhall has traditionally recommended disconnecting coach batteries if staying plugged in for more than a couple days. I disconnect both battery banks before my initial plug in. (on rare occasion, if you plug in and then push the disconnect to store, it wont disconnect, and if you unplug, you will still find the red light to be on and are still connected.)
When I store at home, and am plugged in to 120 AC, once every 3-4 weeks I put the house batteries on “use”- so they are connected and can be charged. I leave them connected for 24 hours and then disconnect them again. This keeps them fully charged, but not overcharged. Check the battery water at least every couple months.
If you have an inverter, for changing your house battery 12 volt DC to 120 volt AC, most of them have a 3 stage battery charger as part of their system, so at least theoretically you have a “high speed, high voltage” first stage, and a “low” voltage trickle which prevents overcharging. There are “charge (battery) wizards” which work off the converter to do the same thing.
Hopefully this will help in understanding what those two red lights by the entry door do.
Doug