Driving around using the 7-pin on the spare battery in the truck bed (via an adapter you invent--not hard to do) is not going to do it for you. amps will be around 5 or 7 amps if you are lucky and in an hour they will taper down some, so think 6AH restored for an hour's drive. Forget that.
You need to run a real battery charger on that spare battery for a fast charge say at 25 to 30 amps initial till it tapers as the battery comes up. How to run that charger?
- Honda gen in truck bed with the portable charger and the battery- run that while driving around---or just park somewhere outside the campground and read a book while the battery gets done.
( your choice on swapping out the spare or leave it in the truck and connect with jumper cables as mentioned )
BTW it takes many hours for two batteries to equalize since the voltage diff is so tiny between the full one and the half full one, hardly any current flows. Tried that one.
-Don't worry about efficiency and losses--who cares? You just want to get it done and keep on camping.
Next method. You can indeed hook an inverter to your truck battery and run the truck engine at idle and that 1000w inverter will run a 35 amp smart charger. But will the campground allow you to idle the truck for an hour? I have used this method and it works great.
The limit there is
- first the inverter has to be able to handle the VA required by the charger. A 35a charger would want about 600w.
-second, the truck alternator has to be able to hold the truck battery voltage up while that draw is on it. When you load the inverter too much, the truck's voltage sags off (BTW turn off the truck's "climate control" so it is not running during this episode reducing what the alternator can handle from the inverter)
So how long are you planning to stay anyway? You get two days per 24 batt, so if you had three 24s you could do six days without recharging any. Just take some extra batteries along and recharge them all when you get home a week later. :) You can plunk the batts down on the ground by the one on the tongue and link them up with jumper cables, so for that time your trailer has three or four (pick a number) batteries. (they don't have to be 24s either, you can use big ones! )
