Triple battery setup run down.

[Cuppa]

I've got mine much like you are describing only I have a crank and aux on the car and two aux on the camper, both on the trailer bum off the aux batt on the car via Anderson plug and I've never had an issue. I've also got a 120w panel for longer stays with plans to purchase a second 120w

Edit:I use a ctek 250 dual on the car

I assume you mean that the two camper batteries are connected to the aux under the bonnet via the Ctek?

[Cuppa]

There are 'many ways to skin a cat' , particuarly when setting up mobile charging systems. All work, but some work better than others. When using battery power for camping aiming for maximum efficiency makes sense as it enables longer overall battery life, & greater camp convenience. Which is chosen is best determined by usage patterns, but more often is determined by the thickness of the wallet. Life is full of compromises. Some better than others.

[megatexture]

I assume you mean that the two camper batteries are connected to the aux under the bonnet via the Ctek?

The ctek is charging the aux under the bonnet then onto the camper via Anderson

As we do trips without the camper I've put the ctek in the car not camper and connect the solar panel to the ctek if needed. When the campers in storage its maintained with a ctek mxs15 so its at max to start with and once we get to our destination the panel is out.

[BigRAWesty]

The ctek is charging the aux under the bonnet then onto the camper via Anderson

As we do trips without the camper I've put the ctek in the car not camper and connect the solar panel to the ctek if needed. When the campers in storage its maintained with a ctek mxs15 so its at max to start with and once we get to our destination the panel is out.

Just touching On what I mentioned before, have you fitted an isolator to the line going to trailer?

[megatexture]

Its used as a Power supply to the rear fuse block for the fridge and other accessories I can't put an isolator on it

[BigRAWesty]

Yea fair enough on that one.

[Cuppa]

The ctek is charging the aux under the bonnet then onto the camper via Anderson

As we do trips without the camper I've put the ctek in the car not camper and connect the solar panel to the ctek if needed. When the campers in storage its maintained with a ctek mxs15 so its at max to start with and once we get to our destination the panel is out.

Aha, so the ctek in the car 'sees' the three batteries as a single unit. How do you manage when camped but have disconnected the vehicle from the camper to go off for a drive? I would wonder if there might be occasions when you want to hook up & drive, immediately after a drive without the camper connected. In which case the aux battery would be fully charged, but the camper batteries would be depleted (from running the fridge etc whilst you had been off driving without the camper). Most times this wouldn't be an issue as given time the three batteries would balance themselves once reconnected. But what happens when you reconnect & drive away immediately? would't the ctek see the aux as charged & not in need of charging, not charging the camper batteries until the voltage in all three had dropped (balanced). This may not be an issue, but I can imagine a possibility where on occasions you stop set up camp & find the batteries are not as fully charged as you need? I suppose it depends upon how quickly the batteries balance themselves & how long you drive for & how long you intend to camp without driving again (The capacity of three batteries would likely give a reasonably sufficient 'buffer' if the next stop was only a short one & the sun was shining). Those three factors could make it a non issue for you, where for some it may be. A fine example of how 'pattern of usage' varies what will work for some & not others I suspect, & a reason to always ask what the pattern of usage is as well as 'what does the user want to run'?

Cuppa

[mudski]

O.k so I keep my SBI12 and buy a dc to dc charger and mount this in the trailer or in the rear of the car? Any recommendations on what charger?

[threedogs]

What are you running that's requires all these batteries??

[mudski]

What are you running that's requires all these batteries??

I have the standard setup in my car. Cranking and Auxilary battery. Our Camper that we have bought will have its own battery aswell. Which will run my 75L combi and a couple of strip lights. I ran my combi for fours days plus two lights on my current 110AH AGM I have, no solar charging too. Was quite impressed really.