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Van Life Tech: leisure batteries, calculating power & what we did in our campervan conversion

DIY cmpervan leisure battery

Van Life Tech: leisure batteries, calculating power & what we did in our campervan conversion

Unless you’re going totally off grid and shutting down all mod cons, you’ll need extra power in your van. And, given you’re on Van Life Income, you’ll likely be wanting to power your laptop fairly regularly to earn some hard cash.

This is a beginners guide to all things electric for your campervan/van conversion. I’m going to give you the answers to questions we had when we started to research this rabbit hole of a topic without any prior knowledge of electrics.

Vehicle / starter battery

Firstly, the power provided by your vehicle battery is required for vehicle specific needs e.g. to start the engine, to turn on the vehicle lights, the indicators, the window wipers, the electric windows, the radio, and maybe most important in the summer…the air con!!! 

Flat starter battery = you’re not going anywhere!

Our vehicle battery (Renault Master)

Although your vehicle battery (sometimes called a ‘starter battery’) may do a fantastic job of all these multi-functions, vehicle batteries are designed for short sharp bursts of electric and not day-to-day van-living where you need continuous flow of power e.g. powering fridges, water-pumps, tvs, mobile phones, laptops and more. Nor do they have the capacity to do so.

The most common method to have more power in your van and also allow you to still have power when you are ‘off-grid’, is to use a leisure battery.  These batteries provide that smooth continuous flow of electricity more suitable to day-to-day living and are separate from your vehicle battery, so no risk of draining it and getting stuck in the middle of nowhere. 

What leisure batteries could you use in a van conversion?

Leisure batteries are 12v deep cycle batteries that can cope with hundreds of discharge cycles and power all your mod cons whilst on the road. There are 4 main types of leisure battery to consider;

  • Lead acid deep cycle battery (flooded)
  • Absorbed Glass Mat (AGM) 
  • Lithium ion
  • Gel 

Each is slightly different in how they work and each has their own strengths and weaknesses. Rather than dive into each, especially when we’re not experts, there’s a great write up on the differences found at Mowgli Adventures.

We went with AGM batteries

Being campervan conversion newbies, we watched countless hours on Youtube and found that most of our fave campervan vloggers were opting for AGM leisure batteries. 

So we did our own technical research to weigh up the advantages and disadvantages of each and found that the AGM would also best suit our needs. 

The positives about AGM batteries that appealed to us:

Like any good battery with positives, there’s also at least one negative, and in the case of AGM batteries the two main ones for us were (1) cost – AGM batteries are more expensive than others and; (2) limited discharge of 50% — lead acid can do 80%.

What this basically means is that you can only use 50% of the battery capacity, or you will ultimately damage it…which also makes them more expensive as you need more capacity 🙁

AGM batteries also need a special charger and are more sensitive to over-charging.

How much power do I need?

Ok, now we need your brain power!

To figure out how much power you might need/want to bring with you, you’ll have to think about the following 3 things:

1/ What electrical devices will I be using?

Here’s an example list of things you might have in your van that will require electric:

  • Lights
  • Water pump
  • Heater
  • Mobile phone
  • Laptop
  • Camera
  • Extractor fan

2/ How much power do these devices require?

The amount of power stored in your battery, is usually measured in ‘ampere hour’ or ‘amp hour’ (Ah). So when you are going to buy your battery, you will be looking at the Ah of each battery

To work out how many Ah you might need, you need to find out how many amps your devices use and ensure this is for DC 12V. You can usually find this information in the manuals, or online, however if they only provide you with Watts, you can work out the number of amps using the calculation below. 

How to calculate Amps, Watts & Volts

When it comes to calculating power, current and voltage, my wee brain likes to think of the WAVE triangle 👋.

This is basically the PIV triangle (Power, Current, Voltage) but easier to remember in my opinion! (Pop Quiz: Current is actually represented in equations by the letter “I”. The reason is Intensité de Courant or Intensity of Current…now commonly called Current).

I simply visualise the WAV…and out pops the calculation!

Amps = Watts / Volts

Therefore if the device was 48W, then the amps at 12V would be 48/12 = 4amps.

Here’s a table we made of our devices:

wdt_ID Device Volts Amps Watts
1 Water pump 12 2.4 28.8
2 6 x 2W led lights 12 1.0 12.0
3 Macbook air 12 5.0 60.0
4 Macbook pro 12 5.0 60.0
5 Iphone 12mini 12 2.0 18.0
6 Iphone 12mini 12 2.0 18.0
7 Soundbar 12 5.0 60.0
8 Projector 12 3.0 36.0
9 Chinese diesel heater* 12 2.0 0.0
10 Extractor fan 12 6.7 80.0

* more on the fridge and diesel heater later #pinchofsalt!

3/ How long will you be using these devices for each day?

In order to calculate the Amp Hour (Ah) battery size you need, you’ll need to figure out how long you intend on using these devices.

A device that uses 1 Amp, running for 1 hour = 1Ah.

A device that uses 1 Amp, running for 2 hours = 2Ah.

Here’s what we calculated for us:

wdt_ID Device Volts Amps Watts Hours per day Amp Hour
1 Water pump 12 2.4 28.8 0.1 0.24
2 6 x 2W led lights 12 1.0 12.0 2.0 2.00
3 Macbook air 12 5.0 60.0 3.0 15.00
4 Macbook pro 12 5.0 60.0 4.0 20.00
5 Iphone 12mini 12 2.0 18.0 1.0 2.00
6 Iphone 12mini 12 2.0 18.0 1.0 2.00
7 Soundbar 12 5.0 60.0 2.0 10.00
8 Projector 12 3.0 36.0 1.0 3.00
9 Chinese diesel heater* 12 2.0 0.0 0.2 0.40
10 Extractor fan 12 6.7 80.0 0.2 1.33
∑ = 55.97

As you can see from the table, if we used all these devices for the amount of time specified for 1 days usage, we would require around 78 Ah. 

As we know, AGM batteries should not be discharged below 50%. Therefore to run all our devices for one day, WITHOUT any method of recharging the batteries,  we would require a battery with double the Ahr. ie we’d need = 2 x 76Ah – around 156 Ah.

What we went with: 2 x 130Ah AGM batteries

Therefore we would have 260Ah to ensure we more than fully covered this, should we ever ‘Wild camp’ for a couple of days. In reality, we’d have our laptops etc fully charged and be operating economically, so we could survive much longer.

If you’re in the UK, we can highly recommend Alpha Batteries and Tayna as great options.

* Chinese diesel heater – this uses a spike of power when starting and a bit extra when shutting down. When running it can be anything between 1-3.5Ah, depending on settings.

* Fridge – we’re not overly confident in these figures and will do some testing in future. There is a MASSIVE difference in fridge power usage and cost. Ours is a decent 48L cool box (not thermostatically controlled). Generally we have it charging whilst driving and off whilst stopped. We also position it in a fairly cool location.

How do I charge my batteries?

You’ll want to have at least one means of charging your batteries, if not more. Here’s some ways you can keep those batteries topped up:

1/ Charge from mains electricity use a smart charger
These are cheap, starting around £30, you can bring your batteries into the house, and just charge them plugged into your house mains electricity or run an extension lead to your van either ‘on site’ or at home, so you don’t have to move them (NB high capacity leisure batteries can be heavy, ours are 30kg each!).

2/ Charge them as you drive
There are various devices you can get to attach to your vehicle to charge the battery whilst your on the move!  We’ll let you research these in your own time, as they are specific to the type of vehicle / alternator you have. 

3/ Solar power
Harness the free power of the sun!  This is a whole other topic that we will delve into in the future.  It entails buying solar panels, and some devices to enable the power to safely flow to your batteries, whilst ensuring it doesn’t overcharge them. 

What we went with
To get started, we went with #1 and #2.

For #1, we have a standard 240 AGM battery charger which we plugin to an extension cable when onsite. So far, we’ve not had to use it at home, except fo the initial charge.

For #2, we have a Voltage Sensitive Relay (VSR) between our vehicle battery and leisure battery. As we drive, the leisure batteries charge. The VSR itself was only £30 so it was a cheap and cheerful way of ensuring we could charge from our vehicle.  So far we’ve been thoroughly impressed by this device, however note that it is not suitable for all vehicles (broadly speaking vehicles manufactured after 2010 tend to  have a ‘smart alternator’ require a different system).

For #3, we haven’t decided yet – not a priority in Ireland 🤣. Just kidding. We are looking into it and will do a separate post on solar power once we decide on the panels etc and install them.

No inverter

We also went 100% 12V — we have no inverter.  The reason is that it makes us think more about our power usage and prevents us using power-hungry devices. We also discovered 12V chargers for our laptops that should be much more efficient than stepping up/down with an inverter.

So that’s a wrap for now! We’ll look at fridges and solar a bit more closely another time.

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