Our Electrical System

Our Electrical System

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“We’ll just put a new battery, maybe bigger, and we’re done!”

That’s what we thought when we brought Elsie home and we plugged in the EHU to check that inside all the 12V and 230V appliances were working.
In fact, everything seemed to be in order…how wrong we were!

We accessed the battery room to check the state of our leisure battery and we found out the terminals were in awful conditions, not really something that makes you think: “this guys must have really taken good care of the motorhome!”.

On top of that the battery was running barely 10V and that was after 2 hours journey and while connected to the external hook up point.
The situation was pretty clear: our leisure battery wasn’t charging neither with the engine alternator or with the built in 230V charger.

electrics_old battery
What we found when we had a look at our leisure battery

At this point we had to start from scratch so we started to write down what we needed from our electrical system and to do some research for all the parts involved.

Took us a while to sort everything out. We tried to save as much as possible from what was already installed but although there’s always room for improvement we can say that so far we’re happy with what we’ve achieved. 

Let’s have a closer look at it:

The heart of our system is a Fogstar 280Ah lithium battery.


lithium battery

I don’t want to go too deep into it because there are lots of articles and info about it on the internet and is one of those hot topics which leads to hours of virtual fights on what’s better. 

The only thing I want to say is don’t take as granted that having a lithium battery is always the best option because that depends on your needs and what’s your specific use.

So do your math first and then decide what’s best for you.

In all our previous experiences with campervans and motorhomes a good AGM battery has always been more than enough but our main use was on weekends or 10/15days roadtrips where the engine was always running everyday (not less than 50/100miles). Now our situation is different, we’re looking at traveling for months with much less daily mileage. We’re also going to use way more power as we now have a tv and other devices such as computers and cameras we use everyday to work so that’s what this set up is based on.

Keep in mind that a lithium battery offers not only great performances but it also weights considerably less than a lead-acid battery. For example our battery weights only 26kg and offers around 240Ah of usable capacity. To have the same capacity with an AGM battery we would need a 480Ah battery pack. When we did our research that meant having 2x260Ah AGM batteries for a total weight around at least 100kg and of course we needed room for 2 batteries. In a 3.5t motorhome as ours saving 80kg is huge so make sure you take that into account too.  

Anyway, back to us, we want to keep the battery charged using the alternator while the engine is running and using a 230v charger when connected to the external hook up.

We will install a solar panel later, allowing us to be completely offgrid.

Charging using the alternator

Ok let’s have a look at what we use to charge our battery while the engine is running.

We installed a dc/dc charger between our engine battery and our leisure battery. It basically takes the current/tension coming from the alternator and adjust it accordingly to what the battery needs to be charged or kept charged properly.

When you’re looking at a DC/DC charger you have to keep in mind that your lithium battery can take a higher charging current compared to a lead-acid battery (we’re talking about 40/50% of its capacity while for a lead-acid is around 10/20%) but you need to check that your alternator is happy with that.

As a rule of thumb you should use a dc/dc charger with an outlet current around 50% of your alternator output and that’s to avoid to stress your alternator.

Our alternator is only a 55A so that’s the reason why we chose a dc/dc charger with only 18A output.

There is also a fuse close to the engine battery and an isolator switch before the charger.

Charging using a 230V charger

When connected to shore power using the external EHU our battery charger is taking care of the leisure battery.

There’s not much to say about this, just make sure you buy one which is compatible with lithium because the charging curve is different from lead-acid.

We’ve got ours from Fogstar and to be fair does its job, the only thing I would say is that the fan is quite noisy compared to other chargers (Victron for example) but being buried under the wardrobe makes it absolutely bearable and not a problem at all.

Priority switch

Let’s keep talking about the 230V system, in particular about a really nice device which plays a key role in our electrical system: the priority switch!

To understand better why it’s so important let’s take a step back and have a look at how our system works.

As I said before we have few things working at 230V only and we need to be able to use them without being hooked up somewhere (especially the fridge, which is running 24/7).

To have 230V we use a 1000W inverter connected to our leisure battery.

Our 230V system is managed by the motorhome built in power unit. I’ve just taken off the battery charger and re-adjusted the wiring to fit the new set up.

We feed it using the inverter when we are offgrid and using the shore power when we are hooked up.

Now here’s where we need the priority switch.

Basically we connected our inverter and our hook up to it and it will take the power from hook up when available or from the inverter when is not.

There is one thing though that we don’t want to power with our inverter and that’s the battery charger because as you can imagine is pointless using the battery to charge itself.

Then again the priority switch comes to our aid. In fact it has an output designed for those things that you want to use just when connected to the external EHU. Such a clever thing!


The inverter is what we use to create 230VAC current using our 12V DC battery.

We are using a 1000W Renogy pure wave inverter. We suggest to always buy a pure wave inverter if you’re using it with electronic appliances such as laptops because other types of inverter (e.g. modified wave) can create some damage.

Our inverter is taking care of the fridge when we’re offgrid so it’s always on. Remember that just having the inverter on is drawing power from your battery. 

Whenever possible is always better to use appliances which work at 12V because would be more efficient than convert it using an inverter. We chose a 230V domestic fridge because it fits perfectly where the old fridge was and we paid just £30 for it: was the most convenient choice but not the most efficient!

Battery monitor

The last part of our system is the battery monitor.

Now, having a reliable battery monitor I think is very important to keep everything under control.

We chose a Victron Smart Shunt, very easy to install and using the app we can check our battery from anywhere inside the motorhome (bluetooth range is around 10 meters)

It’s fitted between the negative terminal of the battery and the negative of the electrical system and it needs just to be connected to the battery positive with the cable provided.

After opening the app you can set your battery parameters and you’re ready to go.

As said at the beginning we’re soon gonna fit a solar panel with its controller and I’ll update the post with all the new mods.

For more info check out the video we posted about this on our YouTube channel and feel free to write to us in case you have any questions

What we used:

Here’s the list of all the parts we used for our electric system.

The amazon’s links are affiliate link so if you’ll buy the product using our link we earn a commission and will be used to support this project and our travels.
Your final cost will not change.

Battery: https://www.fogstar.co.uk

Priority Switch: https://www.ebay.co.uk/itm/185854366026

Battery charger: https://www.fogstar.co.uk

DC/DC charger: https://amzn.to/48ORNoU

Inverter: https://amzn.to/48KVJH6

Battery monitor: https://amzn.to/3VfAn1s

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