What Size Leisure Battery Do I Need?

Rest easy, for the Off Grid Power Geek is here!

We’re diving into leisure batteries in today’s big exploration. Specifically we’re answering the question:

“What size leisure battery do I need?”

Since you’re asking that question, you’re either potentially coming to the end of your existing leisure battery’s life, and you’re wondering what size of battery you should get.

Or you’ve got a new campervan or caravan and you want to know what capacity of battery you’ll need. Maybe it’s even your first vehicle like this, and you need to know how to work out how much power you’ll consume.

Whatever your situation, you’ll want enough battery capacity (measured in Ah) to meet your needs, without overpaying and getting a much bigger battery than you need.

So let’s work it out together! By the end, you’ll know exactly what battery size you need.

What size of leisure battery do I need

What Size Leisure Battery Do I Need: The Lowdown

Let’s check out the factors that affect the size of the leisure battery you need.

The first thing to be aware of is this:

Not all leisure batteries are made equally

By which we mean, the different types of leisure battery have different usable capacities.

What is the usable capacity of a battery? It’s how much of a battery’s capacity you can use on a charge cycle and still keep the battery in good health.

The table below gives the approximate usable capacity of different battery types.

Battery TypeApprox. Usable Capacity
Flooded Lead-acid (the most common lead-acid type)50%
Lithium (LiFePO4)90-100%

As you can see, a battery has different usable capacities for the different battery types.

For example, a 100Ah battery has the following usable capacity for each battery type:

So, to ensure a lifespan, you can only use 50Ah of a lead-acid battery’s capacity on each charge cycle.

But with a Lithium battery, you can use almost the entire 100Ah capacity.

FYI, here are the best Lithium leisure batteries for motorhomes, campervans and caravans UK, and the best 200Ah LiFePO4 battery in the UK.

As for lifespan, here’s how long lead-acid leisure batteries last. Lithium batteries last much longer than that.

Now you know the concept of usable battery capacity, let’s now check what battery capacity you actually need.

How many Ah do I need for my leisure battery?

Here’s exactly how to work out how many Ah your leisure battery needs to have to meet your power needs.

How many Amp-hours (Ah) of power you need from your battery depends on 2 things:

  • How much power you need per day.
  • How much time you’ll be off-grid (the time that your campervan, caravan, or motorhome will be away from a source of power).

How much power you need depends on what electrical devices you use, their wattage, and how long you use them for.

And how much time you’ll be off-grid depends on your travelling plans, whether you’ll spend most of your time on a campsite (with EHU charging available) or whether you’ll be travelling and staying in places without power sources available.

Here’s how to work out what size of battery you need:

1) Work out what your average power consumption, in Ah, will be per day

Here are some approximate values for the Ah used up per day for typical devices you may have:

Electrical DeviceAh Used Up Per Day
LED lighting (eg. 4 hours per day)4Ah
12V Compressor Fridge (running all day)50Ah
Water pump2Ah
Charging devices4Ah
Microwave oven (230V – through inverter)2Ah

This represents moderate usage of electrical devices, not particularly low nor high.

The total Ah used up is 73Ah.

A common size of leisure battery is 100-120Ah, some people will buy two, thus creating a battery bank of size 200-240Ah. Many people with moderate power usage, and who are regularly but not spending every moment at a campsite with EHU choose this size of leisure battery bank.

Let’s say you have a 200Ah battery bank. If it’s a Lithium battery your usable capacity is around 180Ah. If it’s a lead-acid battery, your usable battery capacity is around 100Ah.

If your power usage was 73Ah, in this case you could spend 2.5 days (or 60 hours) away from charge, if you have a Lithium (LiFePO4) battery bank.

If you have a lead-acid battery bank, you’ll have 1.4 days away from mains charge, or 34 hours.

How can you calculate the Ah you will use up per day?

It’s not very difficult, it just requires a little effort.

Just check your appliances and get their wattage. Then make a table like the one below and you can work out the Ah you will use per day on each device.

Electrical DeviceWattage of Device (Watts)Voltage (Volts)Amps used per HourHours used per dayAh used per day
Fridge50W12V4.2A16 (Since compressor is not always running)67.2Ah
LED Lights6W 12V0.5A42Ah

If you check the user manual of a device, it may tell your the number of Amps it consumes per hour, then you can enter this directly in the 4th column.

If not, then calculate the Amps used per hour, by the following formula:

Amps per hour = Power / Voltage

2) How many days would you like to be able to stay off-grid?

(Just in case you’re not clear on the term off-grid, it means being away from any source of power that can charge your batteries (such as the EHU – Electrical Hook Up – charging at a campsite).)

If you have no need for off-grid power

If you don’t need longer than a day away from mains charge, you can get a relatively small leisure battery.

For example, let’s say your power consumption is moderate, at 71Ah per day.

You effectively just need a battery that will provide your electrical devices for a few hours. An 80 Ah battery, for example, only has around 72Ah usable capacity for LiFePO4 batteries, and 40Ah for lead-acid batteries. But that will provide enough power so that you’re covered during the journey to and from the campsite, and in case there’s some problem with the campsite power.

If you need off-grid power

Let’s say your travels will sometimes take you away from mains charge for 3 days, for example.

Your power requirements are 73Ah per day. You need 3 days of power so your total Ah usable capacity needed is 3 x 73Ah = 219Ah.

In this case you’ll need a 300Ah Lithium battery bank or a 500Ah lead-acid battery bank.

300Ah Lithium battery usable capacity = 300Ah * 90% = 270Ah

500Ah Lead-acid battery usable capacity = 500Ah * 50% = 250Ah

As you can see, if you want to go three days off-grid, you’ll need a fair size of battery bank!

If you have solar power and there’s a decent amount of sun, you can rely on that power topping up your battery, so you can get a smaller one.

Similarly, if you have a DC-DC, or battery to battery charger (here’s what a DC to DC charger is), you can charge your auxiliary / leisure battery, using the power from your vehicle alternator, while you drive. They’re cracking bits of technology. The top models, like the CTEK D250SE, with built-in MPPT, allow you to charge the leisure battery with solar power as well.

Most people will tend not to go so long away from mains power, so for many caravan, motorhome and campervans 150-250Ah of battery power is more than enough.

If you’ve considered your power needs and feel a higher voltage is necessary; here are the top 24V 200Ah Lithium ion batteries UK. And, while we’re at it, the best 24V 100Ah Lithium ion batteries.

What Size Leisure Battery Do I Need Summary

There you go!

There’s the answer to “What size leisure battery do I need?”.

We discussed the different battery types and how they have different usable capacities.

You need to calculate the usable capacity of the battery to see if it’ll meet your needs. For example, 50% of the capacity of a lead-acid battery is usable capacity. Whereas 90% of the capacity of a Lithium (LiFePO4) battery is usable capacity.

Then you can work out roughly how many Ah you need for your leisure battery. You can calculate that based on how much Ah each electrical device consumes per hour; then using an average number of it hours it will probably be used each day. This way, you’ll know how many Ah you’ll consume per day.

Then, consider how long you would potentially need to spend off-grid. If it’s up to 3 days then you’ll need a leisure battery with a usable capacity of 3 times your daily Ah consumption.

Good luck with your leisure battery, hopefully you now know the size you need.