Calculate your daily consumption in Ah in five minutes – and find the battery size that suits your motorhome, boat, or solar power system.

The most common question we get is: how large a battery do I need? The answer depends on how much power you use and how long the battery needs to last before it is recharged. Here is a simple method you can use to calculate it yourself.

1. List your consumption

Make a list of everything running on the battery, note the power in watts (W), and how many hours a day it is turned on. The power is typically found on the nameplate or in the manual.

Consumer	Watts	Hours/day	Wh/day
Compressor fridge	45	10	450
LED lights	15	4	60
Water pump	60	0.5	30
Charging phones and computer	60	2	120
Total			660 Wh

2. Convert to Ah

Divide the total consumption in watt-hours by the battery voltage. In the example above with a 12V system: 660 Wh ÷ 12.8 V ≈ 52 Ah per day.

3. Multiply by the number of days without charging

If you need to get by for two days without shore power or solar, you need approximately 104 Ah. Add 20% as a buffer so you do not run the battery completely down: approx. 125 Ah. Here, a 12V 150Ah LiFePO4 battery would be a good choice.

Why lithium can be smaller than lead-acid

A LiFePO4 battery can use almost its entire capacity, whereas a lead-acid battery should preferably not go below 50%. A 100Ah lithium battery therefore provides in practice about the same as a 200Ah lead-acid battery – at less than half the weight.

Remember the inverter

If you use 230V equipment via an inverter, add approximately 10% to the consumption for the inverter's own losses.

Find your battery

See our 12V lithium batteries or 24V lithium batteries. If you are in doubt about the calculation, please contact us – we are happy to help you size your system.

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Autocamper Guide Lithiumbatterier

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