Because of running a PC in my van I need a fair amount of battery power. After quite a bit of thought I decided to go for four 100ah batteries.

My calculations for working out how much power I would need were based on being able to be completely self sufficient for 3 days without any charging. These figures allow for when the weather is terrible and there is no charge to speak of from the solar panels.

Here is what I need to power and the amount of watts that will be used:

Van PC – 17w per hour – 15 hours per day = 255w

Monitor – 18w per hour – 15 hours per day = 270w

Car Radio – 18w per hour – 5 hours per day – 90w

Water Pump – I’ll allow for 50w per day

Lighting – All LED so I’ll allow for 50w per day

Everything Else – I’ll allow 100w per day

That’s a total of 815w per day. To work out how many amps I’m going to use, I divide the watts (815) by the volts (12.5 roughly in a camper van) and get 65 amps. This means over 3 days I will consume 195 amps. Leisure batteries should only be discharged to 50% so I need 390ah of batteries. In reality I probably wont use this much power but better safe than sorry, so 4 x 100ah batteries it is.

The next problem was where to put them. After a little research I found that quite a few people had fitted two batteries under the drivers seat of a Ducato/Relay/Boxer. As my passenger seat is the same it stood to reason another two batteries would fit under that seat. I did some measuring and ordered 4 x Numax 100ah batteries which should fit perfectly.

The next problem was how to wire them up. I wanted them all to discharge and charge at the same rate so they all get the same amount of wear. This was not as easy as it sounds but eventually I was directed to an excellent article here which explains how best to achieve this. This is how I wired the batteries:


The Numax leisure batteries are very good value and I couldn’t find any specific moans about them from people who had them. I would have loved to go all out and buy something like Trojan batteries but the cost was just to much with everything else I need to buy. I figure if the Numax only last a few years I’ll buy some better ones then.

The batteries have now arrived and here they are fitted in place.


The picture above is taken from the back of the seat. They are an almost perfect fit pushing up against the metal bracket at the bottom of the picture and also against a bar at the front. Width wise they sit between two raised bars in the floor design of the Boxer.

To make sure they can’t move around when going over bumps etc I’ve added a cargo strap over each battery. I tried moving them by kicking them from all sides. They don’t move at all.


The above picture is taken from the front of the seat and shows how much clearance there is between the battery terminals and the underside of the seat. Obviously it’s important that the terminals can not come into contact with any metal under the seat so I’m using proper rubber battery terminal covers.


I’ve used 25mm cable with lugs soldered to the ends and then heat shrunk.

I’ll go into more detail on the electrical set up in a future post, this was just about the batteries.

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