In my short time here, I've not seen this approach to charging the trailer battery
from the TV, so I thought I'd share it.
The device is a DC-DC inverter that takes the voltage from the TV and modulates it up or down to act like a smart charger for the trailer battery
. Typically trailer batteries are just wired to the TV via an isolator or relay and you get what you get at the trailer battery
as far as voltage is concerned. If the wiring is too light
(which is often is) you don't get a full charge.
DC Input Battery Chargers for Lead Acid and SLA Batteries, for charging batteries from vehicles and other low voltage sources
The bad news is the $150 price tag and 7.5amp maximum, but it might work for some users.