How to Size a Campervan Battery
This guide explains how to size a campervan battery properly for real 12V use. Learn how to estimate daily power demand, account for battery type, allow for off-grid days, and choose a battery size that suits your fridge, lights, charging devices, inverter loads and travel style.
Why sizing your campervan battery properly matters
A campervan battery should be sized around how the van is actually used, not just around a rough guess or what worked in someone else’s build. If the battery is too small, it will run down too quickly and daily use becomes frustrating. If it is too large, the system may cost more and weigh more than necessary.
The aim is simple: choose enough usable battery capacity to cover your normal daily demand, with a sensible margin for real-world use.
- support the appliances you use every day
- avoid running the battery flat too often
- match the battery to your charging system
- make off-grid use more reliable and predictable
Start with your daily power usage
The first step is to list what your campervan battery will actually power. This usually includes a mix of 12V devices and sometimes inverter-powered appliances.
Common daily loads include:
- compressor fridge
- LED lighting
- water pump
- diesel heater fan
- USB charging
- laptop charging
- router or Wi-Fi equipment
- small inverter loads
Once you know the devices, estimate how long each one runs over a typical day. That is what turns a simple appliance list into a real battery size calculation.
Step-by-step battery sizing method
1. List the appliances
Write down each device that will draw from the leisure battery.
2. Estimate daily runtime
Estimate how many hours each device runs in a normal day. Fridges cycle, lights may run only in the evening, and heaters are often seasonal.
3. Convert to daily amp-hour use
Multiply the current draw of each item by the time it runs. Add everything together to get a daily amp-hour total.
4. Check usable battery capacity
Do not size the battery from rated capacity alone. AGM and lithium batteries provide very different usable energy in practice.
5. Add a sensible margin
Battery sizing should allow for colder weather, heavier days of use and real-life inefficiencies.
Visual example: turning daily use into a battery size
A practical campervan battery calculation starts by adding together the daily energy use of your main devices. This helps turn a vague idea into a realistic battery size target.
Example campervan battery calculation
Here is a simple example of daily energy use in a moderate campervan setup:
| Appliance | Typical Use | Estimated Daily Use |
|---|---|---|
| 12V fridge | Running all day with cycling compressor | 40Ah to 50Ah |
| LED lighting | Evening use | 6Ah to 10Ah |
| USB charging | Phones and small devices | 5Ah to 10Ah |
| Water pump | Short occasional bursts | 2Ah to 5Ah |
| Diesel heater fan | Cold weather use | 5Ah to 15Ah |
A setup like this may easily need around 60Ah to 90Ah of usable energy per day, depending on weather and travel style.
Usable battery capacity matters more than rated capacity
This is where many campervan battery calculations go wrong. A battery may be rated at 100Ah, but not all of that energy is usually considered practical to use.
- 100Ah AGM battery typically gives around 50Ah usable capacity
- 100Ah lithium battery typically gives around 90Ah usable capacity
That is why a 100Ah AGM and a 100Ah lithium battery do not feel like the same battery in real campervan use.
How battery type changes the size you need
Battery chemistry affects how large the system needs to be. AGM batteries are cheaper to buy, but lithium batteries usually provide more usable capacity, faster charging and better performance under load.
| Battery Type | Typical Usable Capacity | General Effect on Sizing |
|---|---|---|
| AGM | About 50% of rated capacity | Usually requires a larger rated Ah battery for the same real use |
| Lithium | About 90% of rated capacity | Often allows a smaller rated Ah battery for the same real use |
This is one reason many campervan owners move from AGM to lithium when upgrading for longer off-grid trips or heavier electrical use.
How many days off-grid do you want?
Battery size is not just about one day of use. You also need to decide how much autonomy you want between charging opportunities.
- 1 day suits travel with regular daily driving
- 2 days suits mixed touring and occasional stationary camping
- 3 or more days suits more serious off-grid camping
If your daily energy need is 70Ah and you want two days of autonomy, you need far more usable capacity than someone who drives every day and recharges regularly.
Visual comparison: one-day vs multi-day battery sizing
The number of days you want to stay off-grid changes the battery size requirement quickly. A system designed for overnight use may feel far too small during longer stopovers.
How solar and driving affect battery size
Battery size cannot be considered on its own. The charging system changes how much stored energy you need. If the van is driven daily or has a good solar setup, the battery may not need to cover all daily use by itself.
- daily driving helps reduce battery size requirements
- DC-DC charging improves recovery while travelling
- solar can reduce battery demand during daylight hours
- winter and poor weather reduce solar contribution significantly
A summer touring setup with daily driving may need much less battery capacity than a winter off-grid setup parked in one place.
Inverter use changes battery size dramatically
Inverter-powered appliances can increase battery demand much more than many people expect. Small 12V loads such as lights and phone charging are one thing. Running mains devices through an inverter is something very different.
- inverters create conversion losses
- mains appliances often pull high current from a 12V battery
- short use of high-power devices can consume a lot of stored energy
- inverter-heavy systems usually need larger battery banks
Typical campervan battery sizes explained
The table below gives a practical guide to common leisure battery sizes used in campervans. These are not strict rules, but they help show where different battery capacities often fit.
| Battery Size | Typical Use Case | General Suitability |
|---|---|---|
| 100Ah AGM | Simple weekend use | Basic loads, lighter use, modest budget |
| 100Ah Lithium | Moderate touring setup | Fridge, lights and charging for more regular travel |
| 150Ah to 200Ah Lithium | Serious campervan setup | Stronger off-grid use and better autonomy |
| 200Ah+ Lithium | Heavy daily demand | Inverter use, extended off-grid travel, larger electrical systems |
Common mistakes when sizing a campervan battery
- guessing energy use instead of calculating it
- using rated Ah instead of usable Ah
- forgetting fridge demand over a full day
- ignoring inverter-powered appliances
- not allowing for winter use or poor charging days
- copying another build without checking your own travel style
Many systems that feel too small were not badly built. They were simply sized using assumptions that were too optimistic.
Use the battery runtime calculator
The easiest way to size a campervan battery more accurately is to use a runtime calculator based on your real appliance use and battery type.
Open Battery Runtime CalculatorRelated campervan battery system guides
Calculate the right campervan battery size
Use the MKGT battery runtime calculator to estimate the battery capacity your campervan setup actually needs based on real daily use.
Open Runtime CalculatorElectrical installation safety notice
This guide is provided as a general reference for sizing campervan leisure batteries in 12V electrical systems.
Correct battery size depends on daily energy use, battery chemistry, charging system design, inverter demand, seasonal conditions and how long the vehicle is expected to remain off-grid.
Battery sizing should always be considered together with fuse protection, cable sizing, charger compatibility and the overall installation layout.
Always confirm manufacturer specifications before installing AGM or lithium batteries into a campervan electrical system.