Leisure Battery Size Calculator – What Size Leisure Battery Do I Need for My Campervan?

Angela Devaney

Choosing the right size leisure battery for your campervan is key to ensuring your electrical system runs efficiently and reliably. Whether planning short getaways or living off-grid full-time, this guide will help you determine the best battery size based on your power needs and usage patterns. 

Understanding Leisure Batteries

A leisure battery is designed to provide a steady flow of power over an extended period. Unlike a car battery, which delivers short bursts of energy, a leisure battery powers campervan appliances like lights, fridges, and chargers. 

Leisure batteries are built to handle deep discharges, meaning they can be drained and recharged repeatedly, making them ideal for off-grid campervanning.

Why Battery Size Matters

The right size battery ensures that your campervan appliances run smoothly and prevents power shortages. A battery that’s too small will lead to frustration, while an oversized battery may add unnecessary weight and cost. 

Also, your total power usage only gives you a rough indication of the minimum battery size required. Other factors, such as charging capacity and seasonal usage, should be considered to ensure you don’t run into issues.

Leisure Battery Size Calculator

Enter your campervan’s system voltage and your appliance information and we’ll calculate the minimum size battery bank you need.

Appliance Name
AC or DC
Power Rating (W)
Hours per Day

Total Daily Energy Consumption

0 W

Minimum Battery Bank Size

Lithium

0 Ah

AGM

0 Ah

How to Calculate Your Power Needs Manually

Start by listing all the electrical devices you plan to use in your campervan, such as lights, refrigerators, water pumps, phone chargers, and heaters. Each device will have a specific power consumption, usually listed in watts (W). 

If it's not listed, use this calculation:

Watts (W)=Volts (V)×Amps (A)

Multiply each device's wattage by the number of hours you'll use it each day to estimate your daily energy consumption in watts. 

For a deeper understanding of how watts, amps, volts, and ohms work together in your campervan's electrical system, you can read our guide on Understanding Watts, Amps, Volts & Ohms.

Accounting for AC Devices and Inverters

If you're using AC devices, they'll need to run through an inverter, which converts DC power from your battery into AC power. This process isn't entirely efficient, and there's a conversion cost of about 20%. 

Additionally, inverters consume some power even when idle, so factor this energy use into your battery calculations.

For example, if an AC appliance draws 100W, the inverter will consume approximately 120W to power it. 

Plus, the inverter counts as an appliance, so include its zero load power rating as a separate device in your calculations.

Factoring in Seasonal and Occasional Appliances

Consider appliances like heaters in your battery sizing, even if you don't use them year-round. Although you might not need your heater in the summer, it's essential to plan for power-hungry appliances during the colder months. 

Always size your battery for the highest seasonal power demand to ensure you have enough capacity when you need it most.

Usable Battery Capacity

Not all batteries can be fully discharged without reducing their lifespan. The usable energy depends on the type of battery you choose:

  • AGM and Gel batteries: Can be discharged up to 50%, meaning a 100Ah AGM battery gives you 50Ah of usable capacity.
  • Lithium batteries: Can be discharged up to 90%, meaning a 100Ah lithium battery offers around 90Ah of usable power.

When calculating the size of your battery, always consider the usable capacity based on your battery type. If your daily energy consumption is 100Ah, you'll need at least a 200Ah AGM battery or a 110Ah lithium battery.

🔌 Important Charging Consideration

Remember that your battery can only provide as much power as you're able to replenish. If your charging system (solar, alternator, shore power) isn't sufficient, you may need a larger battery bank to store more energy between charges. 

Step-by-Step Guide to Sizing Your Battery

To make things easier, we have a Campervan Battery Size Calculator to help you determine the ideal battery size for your setup. Simply input your appliances and usage, and the calculator will do the work for you.

For those who prefer to calculate manually:

  1. Total Your Daily Consumption: Add up the watt-hours (Wh) for all your devices.
  2. Account for Inverter Losses: For AC devices, multiply their wattage by 1.2 to account for the 20% efficiency loss, and factor in idle power consumption.
  3. Convert to Amp-Hours (Ah): Divide the total watt-hours by your system voltage (typically 12V).
  4. Adjust for Depth of Discharge:
    • For AGM/Gel batteries, divide by 0.5.
    • For lithium batteries, divide by 0.9.

Adding a 10% buffer to your total is a good idea to cover inefficiencies and unexpected usage.

⚡ Watch for Power Losses in Inverters

When using AC appliances with an inverter, remember that about 20% of energy is lost in the conversion from DC to AC. Make sure to factor this loss into your calculations to avoid running out of battery power too soon.

Common Mistakes to Avoid

  • Underestimating Power Needs: Missing or underestimating device power consumption can lead to power shortages. List all devices you plan to use, including seasonal ones.
  • Ignoring Depth of Discharge Limits: Each battery type has specific discharge limits. Consider these to ensure the battery meets your needs.
  • Forgetting About Inverters: Account for inverter inefficiency and idle consumption to calculate power needs accurately for AC devices.
  • Not Considering Seasonal Usage: Factor in heaters and other seasonal devices, even if they’re not used year-round.
  • Overlooking Charging Limitations: Ensure your charging system meets your power demands. If the battery won’t recharge fully each day, a larger battery may be necessary. For more tips, see our article on reducing your campervan's electric demand.

When to Seek Expert Advice

If your electrical setup is complex or you're unsure about sizing your battery, it might be worth consulting a professional. While it's possible to work out the size yourself, an expert can ensure you've considered everything, from power consumption to charging capabilities.

Our campervan electrical design service can help create a custom system tailored to your specific needs. If you'd like help with your setup, feel free to get in touch.

FAQs

Getting a complete list of electrical appliances, devices and components you’ll use in your campervan is the most critical part of sizing the electrical system.

Underestimate it and you may run out of power. Overestimate and you’ll probably spend more money and make your setup more complex than necessary.

Work through your typical day, considering all the appliances you’ll use along the way. Don’t forget any gas or diesel appliances that need power to start them up.

And if you intend to use any AC appliance, remember to include the right size inverter on the list too.

The aim of the calculation to size your campervan's electrical setup so you have enough power storage every day. So, it’s important to consider your most heavy usage day.

Maybe you intend to live in your camper during the winter. Your heating will run for longer and probably your ventilation fan too (it’s the best way to stop condensation). 

You may be living indoors much more and there are fewer hours of daylight than during the summer months. All this adds up to a greater energy demands.

Think it through carefully. It’s not going to be 100% accurate but you can get close enough.

The watts of most devices can be found either printed on the device, in the operating manual or the manufacturer’s website. Sometimes, products list the power usage in current (i.e amps). In this case, convert the amps to watts first.

The way the power is stated on devices isn’t standard. Look out for things like:

  • Power: 12V/2.5A
  • Voltage: 12v Wattage: 25w
  • Amp Draw 12V/DC: 4.2

For some devices, in particular those with battery charging adaptors like camera batteries and laptops, use the input values specified not the output values.

The labels on most appliances state whether it is AC or DC.

Failing that, if it has plug you could use in your home sockets, it is probably an AC appliance.

For calculation purposes, if in any doubt, assume it is AC as this produces a higher number so errs on the side on caution.

The calculator works out the minimum size leisure battery bank you need to power your devices.

However, if you only install the minimum amount of battery, you must have the ability to fully recharge it every day. 

Otherwise, you’ll discharge your batteries faster than you can top them up and end up with flat batteries pretty soon.

If you have a reliable source of recharging, like a hook up facility, you may not need any extra battery.

But if living off grid and rely on charging the batteries from solar panels or the alternator, you may need to consider increasing the amount of battery.

Whatever you decide, there is no point installing a battery bank greater than you can reasonably expect to charge.  

Do I need an inverter?

You only need an campervan power inverter if you want to use AC appliances powered by your deep cycle battery.

If you use AC appliances only when hooked up and use AC sockets on the mains circuit, you don’t need an inverter.

You only need an inverter if you want to use AC appliances powered by your deep cycle battery.

If you use AC appliances only when hooked up and use AC sockets on the mains circuit, you don’t need an inverter. Use our inverter calculator to work out the best size for your needs.

Conclusion

Determining the right size leisure battery for your campervan requires more than just calculating your daily power usage. You'll need to consider inverter losses, charging capabilities, and seasonal appliances. 

Planning for these factors ensures your campervan has a battery that meets your needs. If you'd like further guidance or help with your system design, we're happy to assist.

Angela Devaney - Expert in RV & Campervan Electrics - Mowgli Adventures

Angela Devaney

Angela Devaney, a former IT project management professional, embarked on an adventurous journey of full-time travel, which included touring West Africa in a converted overland truck and converting an ex-military 4x4 Sprinter van into a camper for a five-year South American expedition. She now utilizes her hands-on experience to create practical van life advice as a full-time digital media producer, reaching over a million users annually through her YouTube channel, blog, and newsletter. Angela also lends her expertise as the editor-in-chief of the Campervan Electrics Handbook.

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