Leisure Battery Sizing Guide

Choosing the right leisure battery size is one of the most important decisions when building an off grid power system for a campervan, boat, farm, or cabin.

A battery that is too small will leave you without power, while a battery that is too large can unnecessarily increase cost and weight.

In this guide, we explain in simple terms how to size your leisure battery so it can cover your daily energy consumption and the number of days you want to stay off-grid.

Why’s Battery Usable Energy Important To Consider?

When shopping for a leisure battery, you will usually see batteries rated in voltage (V) and amp hours (Ah).

However, when sizing a battery for an off-grid system, the most important figure is knowing how much energy the battery can store. This is known as the battery capacity and it is measured in watt hours (Wh) or kilowatt hours (kWh).

Additionally, the depth of discharge (DoD) is of equal importance, because together with the battery capacity you can work out the usable energy capacity. Or in simple terms how much of the battery’s rated capacity can actually be used safely.

The reason why this is important is that if a battery is completely discharged, it can be permanently damaged.

Typical depth of discharge values:

• For Lithium batteries it is around 80 to 90% usable
• For Lead acid batteries it is around 50% usable

From the above one can conclude that the usable energy will always be less than the battery’s rated capacity. This will be important to consider when we calculate the daily energy consumption and start sizing our battery to cover it.

How To Calculate Daily Energy Consumption

To estimate the battery size you need, you must know your daily energy consumption.

You can calculate it by listing:

• All appliances you want to power
• Their power rating (watts)
• How long you use them each day

Then multiply power by runtime to calculate energy consumption for each appliance and work out the total to calculate the daily energy consumption .

For example:

Appliance	Power (W)	Runtime (Hrs)	Energy Consumption (Wh)
Fridge	40	24	960
LED lights	10	5	50
Laptop charging	60	3	180
Phone charging	15	2	30
Water pump	50	0.2	10

Adding the values in the right most column gives a total daily energy consumption of 1,230Wh. This means your battery must have at least 1,230Wh of usable energy per day to cover your energy needs.

Tip: Use our Power Usage Calculator to estimate your daily energy consumption quickly.

What Size Leisure Battery Should I Get?

The battery size you need will depend largely on the battery technology and its depth of discharge. Referring to the example above with a daily energy requirement of 1,230Wh might at first glance, suggest that a 12V 105Ah lithium battery would be sufficient. However, once depth of discharge is considered, the required battery capacity becomes larger.

For example:

A 12V 150Ah lithium battery stores roughly 1800Wh, with an 80% depth of discharge, the usable energy becomes 1440Wh which is just enough to cover the 1,230Wh daily energy requirement.

A lead acid battery usually allow only 50% depth of discharge, as a result to obtain the same usable energy, you would need roughly a 12V 300Ah lead acid battery

This highlights why lithium batteries are often preferred for campervans and off grid systems as they provide more usable energy while being lighter and more compact.

Should I Get a Bigger Battery Than I Need?

In many cases, it is a good idea to install a larger battery than your minimum requirement, for example if you need to stay off grid for longer or to handle an unexpected increase in energy use. Or for backup in case of poor weather that can affect energy generation, if relying solely on solar panels.

Having two or three days of battery storage can make your off-grid system far more reliable.

Quick Leisure Battery Sizing Table

Daily Energy Use	Recommended Lithium Battery
500Wh	100Ah
1kWh	105 to 150 Ah
2kWh	200Ah
3kWh	300Ah
4kWh	400Ah

This table provides a quick estimate, but actual battery size may vary depending on system voltage and charging sources.

Common Mistakes When Sizing a Leisure Battery

• Underestimating energy use: Many people forget to include smaller loads like chargers, fans, routers, or standby power.
• Ignoring inverter losses: If you are powering appliances through an inverter, expect around 5 to 15% energy loss.
• Choosing low quality batteries: Cheap batteries from unknown brands often have lower real capacity and shorter lifespans.

Conclusion

Choosing the right leisure battery size depends on several factors:

• Your daily energy consumption
• The number of days you want to stay off-grid
• Your charging sources (solar, alternator, shore power)
• The battery chemistry you choose

For most campervan owners, a 12V 100Ah to 300Ah lithium battery offers a good balance between capacity, weight and cost.

In many setups, the battery works alongside solar panels and a battery to battery charger, which help replenish energy each day.

For stationary off-grid systems where solar is the main charging source, it is often wise to install larger battery banks so you can store enough energy to cover cloudy days.