12 to 6 v battery switchout

1) They sat for just under two months

2) After a couple of years of reading about the 6 v batteries I never saw that they can discharger faster, I wish I had as I might not have done it because my camper is parked where I cannot plug it in.

3) I don't have an "off season" so I guess I'll try to get a solar tender.

3) I have this same kind of  disconnect switch and I keep it set on "off" or "both"

One day I'm going to make it to a rally in hopes of having someone teach me to use my multimeter. I only know how to test the charge on my batteries. This is way beyond my capabilities (honestly, with I can't even read this lol):

" Put your multimeter on the ohms scale and connect it across the switch terminals. You should get an open circuit (or very high ohms) reading with the switch open. Then with the switch still disconnected from the battery  close the switch and measure the ohms again. You should get a reading in the 0 to 1 or so ohms range." Just for fun I put the terms I don't understand in italics.  :)

Ohms scale:  On your meter, you should have a dial with various things like DCV (Direct Current Volts), ACV (Alternating Current Volts - your usual house plugs are 120V AC), DCA (DC Amperes), ACA (AC Amperes), Ohms (May be on the dial as a Greek letter Ω (Omega) which is the symbol for Ohms) and possibly battery test and transistor test functions. Ohms may be divided into 2000k, 200k, 20k, 2000, and 200 Ohms. Your meter may be different. Ohms is the symbol used to measure resistance.

Take the multimeter and put it on one of the Ohms settings. You should have a reading of 1, which indicates that there is no current flowing. Touch the tips together. The digital display should change to 0.00 for digital or the needle should move to 0 on the OHMS scale on a meter with a dial and needle. That is what indicates that there is a closed circuit and that current is flowing. If the reading is anything but zero, then that is the resistance of the circuit.

your battery switch should have three connections. One goes to one battery, one to the second battery, and the third to the load (the trailer wiring). With the batteries disconnected, turn the switch to Off. Put one probe on the terminal that leads to the load. Touch the other two terminals, one at a time with the other probe. The reading should stay at 1 (or very high on an analog meter). Turn the switch to battery 1. Again, one probe goes to the load, the other to the terminal for battery 1. The meter should move to 0 or very close to it. Touch 2 and it should stay at 1. Move the switch to battery 2. Again, one probe goes to the load and the other probe goes to the battery 2 terminal. The reading should be 0 or close to it. Then touch the Battery 1 terminal. The battery 1 terminal should remain at 1. Last, turn the switch to Off. Touch the Battery 1 and Battery 2 connections. The reading should remain at 1. If all these give you the results I mentioned, then your switch is functioning normally. 

I hope this helps clarify for you what was meant.

+1 Same. I do have a reminder every 3 months to check the water.

When we stored our Rpod in a storage facility for a while, we pulled the batteries and kept them on a bench. That was a bit of a pain, as I would put them on a charger periodically. I guess you could also put them on a trickle charger, which is not an expensive proposition.