I'm about to be towing my new 22' Sport with a Tesla Model X. The 22FB ships with a single Interstate Group 24 rated at 80Ah, which makes it a pretty weak contender for any kind of boondocking. Options to extend the battery include all of the usual suspects - Group 27 or 29, double Group 24, 2 or 4 6V batteries, AGM inside the cabin, etc. I spent some time researching those with some frustration, because my TV happens to have a gigantic battery in the floor. It also has a
12V system and a 7-pin connector with pin 4 sending +12V.
There are vehicle nuances that I'm still figuring out - is that pin hot when the car is turned off, for instance? Remember that there is no alternator. The
12V battery in my Tesla is charged from the larger lithium ion battery pack. I tried measuring with a multimeter but it's raining today, plus I need another set of hands to vary the state of the car while I'm at it. But let's forget about those nuances for now, and assume that I can provide a reasonable voltage at the 7-pin regardless of my vehicle's status (I can fool the Tesla into service mode if necessary). Let's say the TV can provide some 14V or higher number, and I run #10 from the 7-pin to my battery on the Sport.
My question is first - does this not imply that I can boondock indefinitely from a battery perspective? My vehicle's battery is approximately 90kWh. If I had just 20kWh available for the trailer, that's about a 1666Ah battery equivalent.
Next, what concerns should I have about battery longevity and health? I'm assuming nothing is managing the charge from the hot pin to the AS battery, correct? Would I need to put something inline like a 3-stage DC charge controller?
How lossy is this style of charging? In other words, would 20kWh at my battery really translate to 10kWh at the trailer? I'm not sure even that would deter me, but I'm curious as far as waste goes.
What else might I be missing? Does this seem feasible to those experienced with this sort of thing?
Many thanks for your thoughts.
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