How to Choose a Camper Service Battery

The service battery is the most important thing to have if we want energy independence in a van.

In this article, I will tell you what is on the market to make you understand which is the most suitable for your use.


What is the camper service battery (BS)?

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 (BS) 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?

  • The car battery (called engine battery, BM) is a Lead-acid battery designed to have a good initial starting point (vehicle ignition) but not to have a slow and deep discharge (now there are also different types of batteries as in the start & stop motors)
  • 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
  • Gel
  • AGE
  • Lithium

1.1 Lead-acid BATTERY

In addition to the common free-acid batteries used as an 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, they are at risk of releasing harmful vapours and sometimes even leaking.
  • 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


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

1.4 Lithium batteries

Lithium batteries are slowly making their way into the recreational vehicle market; the cost is starting to drop, and they are fantastic in terms of weight and efficiency.

I have just installed 2 lithium batteries of 80Ah each (= 160Ah), which have an efficiency equal to 4 batteries of 100Ah AGM or gel and infinitely less weight.

Our experiences

As for the batteries, I have experienced various situations. In my first van in Australia, a ’91 Toyota Hiace, I didn’t have a service battery but a simple inverter connected to the engine battery with which I charged the cell, GoPro 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).

Now, thanks also to collaboration, I have installed 2 lithium RV batteries which, okay, are expensive, but I no longer have to worry about energy and consumption.

The AGM battery is the one I recommend as a service battery for your vehicle if you want to save immediately. Still, I recommend a lithium battery if you want to make a small long-term investment and no longer want to worry about energy.

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 litres, in the case of batteries, it is measured in Ah (Ampere hour).

Okay, 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-litre tank (larger and more expensive) if you only use 5l, but the opposite is also true, that is, do not take a 50-litre tank if you need 150; otherwise you will not have enough.


I’ll give you an example on a practical level to be clearer.

If you have a light bulb that absorbs 6watt and you use it for 4 hours a day, calculate:

Bulb: 6watt x 4 hours = 24 watts per day

You will have to perform this calculation for each piece of equipment you plan to use. Let’s see examples of appliances commonly used in the van by inserting indicative values.

FRIDGE: in this case, you have to be a little careful because appliances such as the refrigerator, even if they are connected 24 hours a day, are not always in operation (unless you use a camping cooler of those with the fan always on ) but they work on average less than 20 minutes per hour (therefore 1/3 of an hour) to maintain the temperature (depends on the type of fridge, outside temperature, how full it is, etc.).

To perform your calculation correctly, you must therefore consider the following:

Twenty minutes per hour x the 24 hours a day = 8 hours of actual operation per day.

So, assuming the fridge draws 40 watts and runs 8 hours a day:

Fridge consumption: 40 watts x 8 = 320 watts per day.

Computer: This is about calculating how long your PC takes to charge and how many times a day you charge it and multiply by watts.

PC consumption: 45 watts x 2 hours (time to charge) = 90 watts per day.

Once you have repeated this calculation for all your appliances, you will have an estimate of how much energy you need each day.

Using the data in the example, we calculate the total (light bulb, fridge and PC):

TOTAL 24W + 320W + 90W = 434watt per day

Since the battery capacity is measured in Ampere hours (Ah) and we have the total in Watts, you can use this simple formula to calculate how many Amps per day you need:

Starting from this formula

Power (Watt) = Voltage (Volt) * Current (Ampere)

We derive

A = Watt/volt

(where the Volts are those of the battery, i.e. 12volt)

So in our example, it becomes:

A = 434/12 = 36 A

Now you know you need around 36A per day. Probably, in reality, they are more because you will also use other equipment in addition to those in the example; if you use the inverter to make them work, this too will have its consumption that you need to calculate (but don’t worry, we’ll talk about this later in the “Inverter” paragraph).

All our example calculation considers one day of autonomy. To be self-sufficient for more than 24 hours, you must multiply the total by the days of autonomy established.

Assuming you want to be autonomous for just one day, logically, you will think well, since I need 36A, I take a 40Ah battery, and I’m fine.

Service batteries should never be discharged more than 40-50% of their capacity; otherwise, they will be damaged.

This means that in a 100Ah battery, you only have 50-60 Ah (or less) available before having to charge it, not 100Ah as it would be normal to think (at least I thought so at the beginning). Returning to the 36A in the example, you will need a battery of at least 70Ah.

To measure the battery charge, you can use a voltmeter. There are different types, from the simplest and cheapest (like this one) to the most sophisticated and expensive (for example).


When choosing the capacity of your battery, 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 every day you will be able to charge it every time for various reasons fully (bad weather, which reduces the efficiency of the monocrystalline solar panels, you travel little, and the alternator does not have time to charge it, etc.)

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

However, we try to load everything we need, such as cell phones, cameras etc., via the cigarette lighter socket of the van, with the classic USB adapter when we are travelling (engine running).

Remember that if you realize later that you need more energy, you can take a larger or a second battery to be connected in parallel with the other.

The fridge is one of the appliances that consume the most, so if you plan to use it often, I suggest you take a compressor fridge, which is the best in terms of cooling and consumption. In this article, I compare some of them to advise you on the best.

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