professer dan, i do not know if my battery voltage drops to 12.1 volts .
i never measure it .
i was an electrician when i was a kid in the late 1960's .
i learned about the refer control being voltage critical within the first dry camping we did in about 1995.
the refer tells me if my voltage is too low .
my rv batteries get charged on 120V the day before each trip and i fully disconnect the rv batts fully charged when i store my trailer .
i did upgrade to AGM Exide Edge for the 2 batts in my pickup.
my rv batts are old but work well . i will find some serious RV batts soon , even though i have no issues now .
we dry camp with others . i stole the 4 battery jumper cable trick from one of the older campers after observing him .
since then we have had never lost our refer controller .
the kind of camping we do always involves at least one other camper .
sometimes 8 or 9 units .
sometimes in a forest service type campground but just as often dispersed camping that is readily available .
a lot of our camping is outside .
we spend our days walking , hiking, mountain biking , in the lake , etc.
we always build large campfires and spend the evening retelling the same old stories until it is time to turn in .
we use the various LED headlamps and lanterns , but always use our propane coleman lantern to take the chill off the travel trailer while getting ready for bed .
we have a propane bottle mr buddy heater that does not use up battery capacity but will heat up our 21T komfort .
in the morning we always boil water on the inside stove for tea / hot chocolate .
this takes the chill off the trailer also.
we often do an early october campout with a big circle of friends .
the campfire runs all day and into the evening and is about a 4 foot diameter .
everybody helps get firewood because we like the warmth and comraderie .
we still do not stay in our trailers much .
we use a couple of EZ-UP Quik-Shades ourselves and so do our friends .
we mostly cook on a coleman stove and a portable grill .
so the trailer for us is just a place to sleep , take a shower , have a clean bathroom , and transport our gear to the camp spot .
we have an aftermarket mattress , use a down comforter , plenty of fleece blankets and are cozy even without 120V .