Breaking Down the Caravan Auxiliary Battery Kit

Caravans are large vehicles with many electrical needs. Generally, their only source of power is the battery. If your caravan depends on one battery for starting, playing music, controlling the lights, and all other necessary functions, you will risk draining that battery in the middle of a long trip.

It is important to ease the workload on your source of much-needed power. Usually called an auxiliary battery, this supports your main battery. For instance, the main battery provides enough power to start the car, while the auxiliary battery supplies power to fridges, phones, fans, TV and other caravan necessities.  

Functions of Auxiliary Battery

Auxiliary batteries, can be used as a starting point and can power electronic components like the start-stop system in a micro hybrid vehicle.

They can also serve as backups in drive-by-wire or brake-by-wire systems, further adding another layer of safety when you drive.

New Auxiliary Battery Kit

Auxiliary batteries come with some specialized equipment that is important in the installation process and overall function of the auxiliary.  Essentially, a good auxiliary battery kit should come with the following:

  • One voltage sensitive relay (VSR).
  • Two battery terminals.
  • Enough copper lugs. Usually, six lugs.
  • Red and black cables of varying lengths.
  • Red and black heat shrinks of different lengths.

Other equipment might be needed, but  depends on your manufacturer.

Understanding The VSR

The voltage sensitive relay or VSR, is important to keep your main and auxiliary batteries charged. It is also used to prevent over-discharging of the batteries.

When you start your engine, the starter (main) and auxiliary batteries are separated. At this point, only the starting battery is charged. When the voltage gets to a pre-set value of 13.3 volts, the VSR connects to the auxiliary battery and also charges it. When you stop the engine and the voltage drops to 12.8 volts, the VSR disconnects both batteries.

This way, your auxiliary battery continuously supplies power to what it is connected to, without affecting, draining or interfering with your main battery.

Why Do You Need an Auxiliary Battery?

Installation is highly dependent on your purpose of getting an auxiliary battery. Knowing why you need an extra source of power is important because it affects the location of the installation. These locations vary, from the boot, under the seats, in front of the bumper to the back of the caravan.  

If you need an auxiliary battery as a starting assist, you can place it right inside the engine compartment. If you need the battery to provide reserve power for other reasons, like powering the fridge and sockets when the caravan engine is not running, it can be installed within the passenger compartment.

Essentially, you should put the battery in the safest place closest to where the power is needed.

Installing an Auxiliary Battery

Installing an auxiliary battery is a simple job. However we highly suggest you leave this kind of job to the professionals.

The following is a step-by-step process of what we do to install an auxiliary battery.

1. Understand the ideal position or location to mount the auxiliary battery. Ensure we make use of battery boxes to keep the battery intact during movement

2. Disconnect the caravan main battery.

3. Make sure the battery kit has just enough wire. The less wire between the auxiliary battery and the VSR, the better.

4. Place the VSR in a position close to the auxiliary battery. We make sure it is placed away from areas that generate too much heat, or where excessive movement takes place. It must also be installed as close as possible to the main battery.

5. Measure out the length of the red cable with lugs at both ends. This is done by stretching the cable from the mounting plate on the back of the VSR to the positive terminal of the starter or main battery. Cut that cable to the appropriate length.

6. Measure out another red cable, and extend it to the positive terminal of the auxiliary battery.

7. Cut away 0.5 inches of insulation on the end of the wire to attach a lug connector. When we attach the lug to the wire, we pass some heat to that connection so they blend tightly together.

8. Here is how we connect the VSR to the starter battery. There is a terminal on the VSR usually marked with a red dot or called “positive sense battery”. That is where the wire from the starter or main battery is attached. Right on the VSR, there is another terminal marked “positive second battery”. We attach the cable from the auxiliary battery to that point.

9. We the earth both the VSR and the auxiliary battery. Usually, there are earth wires – most times, black wires – attached to both the VSR and the auxiliary battery. We earth them by securing them to other engine components with bolts that have been used to earth.

10. Permanently fix the VSR to the mounting plate. This can be done by either drilling a hole and screwing it tightly to the body, at the right place, or using some industrial grade Velcro.

11. Attach the positive cable to the starter and auxiliary batteries.

12. Attach the cables to the negative terminals. Connect to the main battery first, and then to the auxiliary battery.


Getting an auxiliary battery is very essential for your caravan. That way, you don’t run the risk of having a deficient caravan battery.

It is important to install the auxiliary battery properly and to use the correct tools to do so..

That is where the professionals at All Brand Caravan Services come in. Our skilled team will  help you with the installation process and other necessary needs, related to installing your auxiliary battery.

You can send us a mail at or give us a call at (07) 3869 2969 and (07) 3269 5979.

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