12V Guru – Best setup for caravan battery charging

Question to 12V Guru: What is the best setup for caravan battery charging?

Hi Dave,

Can you please advise the best and most cost effective setup for vehicle and caravan battery charging. I have seen two main configurations:

  1. solar panels and regulator mounted on vehicle charging two AGM batteries (one start and one auxiliary) connected to caravan with Anderson plugs and caravan solar and regulator to batteries on the caravan.
  2. DC-DC charger with solar input between start and auxiliary battery on the vehicle and DC-DC charger with solar input for the caravan batteries and solar panels.

Typically fridges in vehicle and caravan are the main power users.



12V Guru answers:

Hi Ray,

The two setups you have described for caravan battery charing sound quite creative in what they are trying to achieve.  I am guessing that there is probably an easier way to setup an adequate solution.  What I am missing from the question is the ultimate goal you have in your setup.  You mentioned in the beginning that you were after the most suitable setup for charging a caravan battery and a vehicle battery. 

The vehicle battery is already managed by the alternator in your car so let’s assume that you mean a deep cycle style battery for powering the fridge that resides in the rear of the car.

Powering fridge with deep cycle battery

Let’s cover this battery first – the simplest solution you could utilise here which is cost effective and best suited to the application is to install a simple DC-DC charger in your vehicle to manage what should be a deep cycle battery.  There could be two possible setups in this scenario – one where the battery is mounted under the bonnet of the vehicle or where the battery is mounted in the rear of the vehicle in a secure ventilated location such as behind a seat or a drawer setup.

Battery under bonnet

If the battery is mounted under the bonnet and setup as a dual battery setup you will need to find a DC-DC charger that is suitable to be installed under the bonnet of the vehicle. This means it will need a high IP rating to withstand dust and water but also must be rated to handle the extreme temperatures that can be generated under the bonnet of a car which is driven for hours through high temperature in outback Australia.

Battery in the rear of the vehicle

The second option is where you select a DC-DC charger that does not hold such a high IP rating and is then mounted internal to the car beside a battery that is stored normally in the rear of the vehicle. In both scenarios you will need to ensure that it is a latest model DC-DC charger than can handle smart alternators installed in modern cars which lower their voltage once the primary battery is charged.

You would only need to install solar on the roof of a car if you were planning to stay in one location for a few days without driving the car and in which case many DC-DC chargers will take both the alternator and the solar as an input to charge the battery in vehicle.

So, in summary – DC-DC charger than handles solar and alternator input.  Use movable panels on Anderson connector to position for best charging.

Charging your caravan battery

It is not possible to have both batteries charged by the same device unless you install some type of isolating switch between the batteries and this is generally not effective. Therefore, you will also need a charging source for the battery in your caravan.  Again, the most cost-effective way to do this is top utilise a DC-DC charger which can handle solar and the charge available from your car.  This time the choice is clear in that you can choose a DC-DC charger with a lower IP rating install right beside our battery.

Set it up with proper fusing and correct wire size from your Anderson plug connection from the vehicle and you should enjoy heaps of charge from either your car or solar panels – fixed or movable.

You could even have the same charger in both setups. Of course, you could move to fancier full power management systems but to get away with a smart, cost effective and highly suitable solution for caravan battery charging – 2 x DC-DC chargers could cover you. There are a multitude of displays and 12V output distributions that need to be considered but you could just run all these directly from the battery.

Safe Travels,

12V Guru

The article was written for Caravan World Magazine.

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17 thoughts on “12V Guru – Best setup for caravan battery charging”

  1. Hi Dave, Can i run my solar from my caravan through my BMPRO System in the caravan through an Anderson plug to BC DC charger with solar availability to my auxiliary battery in the back of my ute to run my ARB Fridge? Saves carrying extra solar panels around might as well use what is on the roof of the van.Thanks Warwick.

    1. Olga kustova

      Good afternoon Warwick,
      To run the fridge only, you are better off putting a positive and negative output from the BP35 for when you are free camping.
      To use the roof solar to your bc-dc would mean you are not charging your caravan battery if you take the solar off the BP35.

  2. Hi team a quick query. I have an Anderson plug at rear of my Pajero to charge a 120amp deep cycle battery in caravan. When testing the voltage at the rear of car I get 14.7v with car running but once connected to caravan battery the reading drops to 12 .35v . Is something wrong or have I missed something?? Cheers and thanks in anticipation.


    Hi, can you advise the most suitable DC-DC charger to install under the bonnet of a 2017 Toyota Prado. This is to charge the ‘onboard’ deep cycle batteries. The Anderson plug is already installed and wired but not connected to a charger. Thanks, Pete

  4. Hi Olga,
    Just to expand on this post a little. I have already set up a dc-dc charger in the back of my car along with a 140Ah auxiliary battery and a car fridge (Waeco CFX50). It will also accept solar charging from my portable 200w panel. This was great for our camping trips under canvas.
    Now I’m about to buy a caravan to go travelling this huge country (when allowed).
    I would like to charge my van batteries via my car while on the road and solar once camped. This will keep my van fridge running.
    Will I need another dc-dc for the van, probably mounted somewhere in the van and run a fused cable all the way from the car battery to an Anderson plug on the back and thence to the van. I presume this will need to be 6B&S cable to minimise voltage drop over that length. Will that be enough? Also, what size fuse am I likely to need close to the car battery?
    Thanks in advance.

    1. Olga kustova

      Hi Kevin,

      Yes, another DC/DC charger will be needed in the caravan as the batteries in the car and caravan are all dissimilar.
      Won’t be able to recommend anything in particular without knowing what Battery management system or battery type you’ve got. In regards to the wiring of cars you will need to speak with the manufacturer and maybe an auto electrician.

  5. Hi, I have a solar panel charging a 140 amp gel battery in the rear of my ranger, I use it to run my waco fridge, but can I hook that battery to my caravan through the grey anderson plug. I already have 2 104 gel batteries in the van with 3 140amp solar batteries.

    1. Olga kustova

      Hi Paul,
      As there are dissimilar batteries in use, there should be a DC/DC charger between the car and the battery in the tray and then another dc/dc charger in the caravan to work with that system and keep it all separate. This is so that all batteries are charged correctly.

  6. I have a jayco with a bmro35 b- l 100 ah battery with 150 solar feeding charge .. now I’ve acquired a Mitsubishi with a bmpro mini boost35 and a 190 ah in Ute .. how do I charge both and be useable in the van .. not needed in Ute while towing.. my thoughts double Anderson plug straight to 100ah battery.. or two Anderson to van and one to aux in on bmpro in van to charge 100 ah other to battery it self

    1. Olga kustova

      Good morning, Darrell,

      By running a lead from one battery to the BP35 yes it may put in some charge into caravan batteries providing there is a minimum of 1volt higher than the caravan batteries and 1 amp of current for the caravan battery to accept a charge. Once the batteries equalise out the charge will stop. The Miniboost will see both batteries as one large battery.

  7. Hi, Just wanting to make sure I will have sufficient power and charging capacity.
    Retreat Fraser on order; Standard 225 Lithium, BM Pro 35, 570watts of Solar, Running seperate Auxiliary battery from Car for charging.
    Van has a Dometic 188ltr Compressor fridge, and I have a 2000watt Redarc inverter for Coffee machine/laptop

    Plan to spend 3 to 4 days at a time off grid.

    1. Olga kustova

      Good morning Wayne,
      The only way to correctly work out your consumption is to work out realistically the times of how long you will use each appliance and do some calculations or even simulate the power usage in the backyard at home. The system does sound like you have enough power, but inverters and coffee machines are extremely heavy loads and will use a lot out of a battery.

      Kind regards,

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