House battery charging options

A 200w solar system, in sunny conditions, will suffice. A second battery would be your next upgrade.

Plugging into your running tow vehicle will generally not charge very quickly; by the time the current gets through all the (fairly small) wires and connectors between the alternator and the trailer battery, you have enough impedance that you'll only get a slow charge. A better option to use the tow vehicle alternator would be decent jumper cables between the tow vehicle and the trailer battery more directly.

An even better option, as mentioned, is a relatively modest solar setup if you'll be camping in a reasonably open area.

Refer should only use 12 volts for control of it. Very little power.
Wiring in tow vehicle is small. Charging through it is not very efficient.
Best overall is to get a genset. A small one would be good for charging battery(ies) but no air conditioning. One something like this genset

DrewE wrote:
Plugging into your running tow vehicle will generally not charge very quickly; by the time the current gets through all the (fairly small) wires and connectors between the alternator and the trailer battery, you have enough impedance that you'll only get a slow charge. A better option to use the tow vehicle alternator would be decent jumper cables between the tow vehicle and the trailer battery more directly.

I disagree with that last statement !

A much better option would be a DC-DC battery charger. Renogy 20A or 40A. $111 - $170 on Amazon

etrippe wrote:
Trailer has 1 12v. battery, and most likely low quality.

When it dies, replace it with two 6V golf cart batteries.

Agreed, leaving the tow vehicle running and connected to the trailer is a horrible idea. Besides being a VERY slow charge, it will burn up too much fuel doing it (ie, it is highly inefficient).

Some RV fridges use 12 volts only for the control board, but some do actually use 12 volts to cool. You need to determine which it is.

Generators are noisy, and will be a pain overnight as well as most unwelcome amongst any neighbors at 2 am. Solar is a much better choice, but it sounds to me like you are going to need a battery upgrade. They put the cheapest 75-80 AH battery possible on new trailers, so, yeah, first step IMHO is putting on a real battery.

naturist wrote:
They put the cheapest 75-80 AH battery possible on new trailers, so, yeah, first step IMHO is putting on a real battery.

I agree with everything, but would say first thing to do is do a trail run with just your current battery power. You can do it at a full hookup campground, just don't plug in. Determine how long your current battery lasts. Then you can figure out the best size battery for your needs. Then you can add appropriate solar for recharging the new battery.

Thanks all. The frig is all 12 volt, no propane or 120 volt. All I want to do is keep the battery charged for the frig, fan and some led lights over night. Solar sounds promising but what if it’s cloudy for a few of the days that we are dry camping?

I’m at home now so I will disconnect the trailer from shore power, turn on the fan and time it till the battery goes down to 1/2. Good idea, thanks

What is make and model of refer?

etrippe wrote:
Thanks all. The frig is all 12 volt, no propane or 120 volt. All I want to do is keep the battery charged for the frig, fan and some led lights over night. Solar sounds promising but what if it’s cloudy for a few of the days that we are dry camping?

I’m at home now so I will disconnect the trailer from shore power, turn on the fan and time it till the battery goes down to 1/2. Good idea, thanks

Rule of thumb is one battery a day using 50AH a day. So your 5 days off grid is going to need some work with only one battery!

If there is no furnace time but is a 12v fridge it should be the same, but if furnace too, you are in a world of hurt for 12v. You will for sure need a generator and recharge the batts you do get/can carry in that RV and will need a proper battery charging converter or charger to do that. Solar can help with that chore, but as you note, the sun might not come out when needed.

Forget about running the truck engine as a generator, that is just for a last ditch way to get some 12v to last a little longer.

etrippe wrote:

I’m at home now so I will disconnect the trailer from shore power, turn on the fan and time it till the battery goes down to 1/2. Good idea, thanks

50% discharge will shorten the life f a lead acid battery.

Two 6V golf cart batteries have about 210Ah, much higher than any single 12V lead acid battery and more than most pairs of 12V batteries.

Buy the DC-DC charger. At 40A it will quickly recharge a battery bank faster than anything short of a 50A AC powered charger. Bonus, you can drive while driving !