DIY van electrical system: everything you need to know

If you are reading this article, it means you are thinking of building an electrical system for your van, van, camper, boat, etc., or at least trying to understand a little more.

In this article, we will explain the fundamental components that make up the electrical system of a recreational vehicle and how to choose the most suitable one for your use.


What is the service battery?

It is a battery that allows you to accumulate the energy you need in your vehicle to use/charge the various equipment you need (fridge, telephone, PC, water pump, lights, TV, etc.).

The battery is, therefore, your energy reservoir.

The service battery must have a slow discharge, that is, designed to be able to supply current for long periods.

In this regard, one of the most common questions is:

Why is it better NOT to use the car battery as a BS?

Simply for two reasons:

  • The car battery (called engine battery, BM) is a Lead-acid battery designed to have a good starting point (vehicle ignition) but not to have a slow and deep discharge
  • If you use it as a BS, you risk being left with the battery on the ground and not being able to start again (with the risk of ruining it)

That said, while you are on the road, with the engine running, you can still use the cigarette lighter socket (which is connected to the BM) to run a 12v cooler or charge the phone without problems.

As long as the engine runs, the BM continuously receives energy from the alternator. Therefore, there is no risk of it being damaged by discharging beyond a certain threshold.

If you need to charge/use your devices even with the engine off or, in any case, in a prolonged and constant manner, consider purchasing a dedicated (slow discharge) service battery.

There are several types of slow-discharge batteries on the market:




Lead-acid BATTERY

In addition to the common free-acid batteries used as engine batteries (i.e., designed for an initial peak only), there are also free-acid batteries designed for slow and deep discharge.

However, they have some disadvantages compared to Gels and AGMs:

  • The acid inside is in liquid form, and due to the chemical reactions that take place inside them, there is a risk that they release harmful vapors and sometimes even leak
  • They need maintenance
  • They have longer charging times than AGM and Gel
  • They have a shorter average life than the other two
  • They must be installed in the indicated position (electrodes at the top) and, therefore, cannot be lying on the other sides (a situation that is sometimes necessary due to space issues)

For this series of reasons, it is the least suitable, but it is still used because of its lower price than the others.


AGM slow discharge batteries are, together with Gel ones, the most suitable for the use we are interested in because:

  • They work very well with slow and deep discharges
  • They have reduced reload times
  • They withstand many charging cycles
  • We can arrange them in any position (standing and lying on the side)

We took a 100AH AGM RV battery.


Gel batteries have more or less the same functionality as AGM batteries but are more delicate than the previous ones.

In reality, there is a fourth type of battery, lithium ones, but they have a hallucinating cost; therefore, we do not consider them.

Our experiences

As for the batteries, we have experienced various situations. In our first van in Australia, a ’91 Toyota Hiace, we did not have a service battery (lithium battery 12v) but a simple inverter connected to the engine battery with which we charged the phones and the PC. We were real newbies and rather confused about the functioning of the electrical system. We have repeatedly found ourselves with the battery completely on the ground (we thank the good heart of the Australians who, on several occasions, have allowed us to continue our journey). So avoid using the engine battery to charge your equipment !!

When we computerized our Opel Vivaro in Italy, we did things right by installing a 100Ah AGM battery from Renogy. It is charged via solar panel and alternator and is sufficient for our consumption needs (we mainly use it for fridge, lights and to charge phones, PCs, and cameras).

We recommend an AGM battery as a service battery for your vehicle.

Finally, in our Nissan Homy in New Zealand (see the video of how we converted it), we have an 85Ah free-acid service battery (purchased and installed by the previous owner) connected to the solar panel and the alternator. We also use it here for the fridge and to charge the various appliances.

Unfortunately, sometimes we are forced to turn off the fridge during the night. This may be because it is slow to charge or other factors (inability to measure the incoming amperage). Having a fridge that only works at 220v, we have the pure sine wave inverter always on, so an 85Ah battery is a bit small, but since we only used the van for a few months, we did not want to invest in other equipment.

Now that you understand the different types of service batteries, it’s time to calculate how much power you need to buy the right size battery.


As I told you before, the battery is your energy reservoir, so all you have to do is figure out how big this reservoir will have to be.

If the size of a water tank is measured in liters, in the case of batteries, it is measured in Ah (Ampere hour).

Ok, but how many amps do you need?

To calculate the energy you need in your vehicle, you need to check the absorption, that is, how much the equipment you intend to connect consumes. You can do this by taking the Watts indicated on the label or instruction booklet and multiplying that number by the number of hours you think you are using it daily

To understand, making a rough similarity, it is useless to buy a 100-liter tank (larger and more expensive) if you only use 5l, but the opposite is also true, that is, do not take a 50-liter tank if you need 150; otherwise you will not have enough.


When choosing the capacity of your battery, please take it as large as at least double the calculated amperage. This is because summarizing what has been explained up to here:

  • You cannot download it beyond a certain value if you don’t want to ruin it (not less than 50%)
  • You may need to connect extra equipment that you did not calculate
  • It is not said that you will be able to fully charge it for various reasons (bad weather, which reduces the efficiency of the solar panel, you travel little, and the alternator does not have time to charge it, etc.)

We use a 100Ah AGM battery from Renogy like this one.

It works well, and for the moment, it is enough for us, given our use (compressor fridge, PC, lights, cell phones, camera).

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