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Campervan Power Audit & Off-Grid Calculator

List your appliances, configure your power setup, and instantly
find out how many batteries and solar panels you need to live off-grid. 100% free tool.

1. My Appliances

2. Leisure Battery Bank (Optional)

3. Solar Panels (Optional)

My Power Audit

Daily Power Consumption
0 Wh / day
Peak Load (if everything is turned on simultaneously)
0 W
Total Usable Battery Capacity
-- Wh
Total Solar Array Capacity
-- W
Off-Grid Battery Life (no sun / no driving)
-- Days

Why Should You Do a Campervan Power Audit Before Your Build?

One of the most common mistakes in van conversions is purchasing your leisure battery and solar panels before knowing what you are actually going to power. A complete power audit (electrical load calculation) is the foundation of your campervan's electrical system. It allows you to:

  • Avoid Flat Batteries: Ensure you won't be left without power after just 24 hours of British rain.
  • Make Your System Safer: Determine your Peak Load (when multiple high-draw appliances run simultaneously) so you can safely size your 230V inverter, fuses, and cable cross-sections.
  • Optimise Your Budget: Avoid spending £1,500 on an oversized 200Ah lithium battery system if your actual power requirements (LED lighting, diesel heater fan, phone charging) can be comfortably met by a standard setup.

For an accurate result, our calculator uses the method trusted by professional auto electricians: calculating energy consumption in Watt-hours (Wh). Unlike Amp-hours (Ah), which fluctuate depending on system voltage (12V, 24V, or 230V mains), Watt-hours provide a universal and reliable unit of energy measurement.

1. Daily Consumption (Your Load)

Multiply the power rating of each appliance (Watts) by the estimated time you use it each day. Example: a 45W 12V compressor fridge running for 8 hours a day consumes 360 Wh/day.

2. Battery Storage (Usable Capacity)

A leisure battery should never be fully drained. A 100Ah lead-acid/AGM battery (1,200 Wh) provides only 600 Wh of usable energy at 50% Depth of Discharge (DoD). A 100Ah lithium (LiFePO4) battery provides 1,080 Wh of usable energy at 90% DoD.

3. Off-Grid Battery Life

Divide your total usable battery capacity by your daily consumption to estimate your true off-grid autonomy in days—representing how long you can last without solar yield or driving to trigger your B2B (DC-DC) battery charger.

🔋 Understand Your Power Audit Results

Now that you know your daily power needs in Wh, learn how to choose the right leisure battery (Lithium LiFePO4 vs AGM) and perfectly size your solar setup with our dedicated guide.

Read the 12V & 230V Electrical System Guide →

Frequently Asked Questions (Campervan Electrical FAQ)

What leisure battery capacity do I need for year-round van living?

For year-round living, including running a 12V compressor fridge, diesel heater, water pump, LED lighting, and charging a laptop, the average daily consumption is estimated between 600 Wh and 800 Wh.
A 100Ah to 150Ah Lithium (LiFePO4) battery (providing 1,200 Wh to 1,800 Wh of total capacity) is generally recommended to give you 2 days of off-grid power without needing to recharge.

What is Peak Load?

Peak Load (or peak power demand) is the exact moment when absolutely all of your electrical appliances are switched on at the same time.
Although this scenario is rare in reality, calculating this figure is essential for safely sizing your electrical system's protection—particularly the size of your main mega fuse, your cable gauges (cross-section in mm²), and the maximum rating of your 230V inverter.

How much solar do I need on a campervan?

A general rule of thumb among UK van converters is to install a solar array with a wattage at least equal to or greater than your battery's amp-hour capacity.
For example, if you have a 150Ah leisure battery, aim for between 150W and 300W of solar panels. Paired with a good quality MPPT solar charge controller, this should reliably recharge your battery bank during a decent day of British sunshine.

Should I switch off my 230V inverter when I'm not using it?

Absolutely! When switched on, an inverter constantly draws a standby (or "phantom") current, even when no 3-pin domestic plugs are connected. This standby draw is often between 1A and 2A, depending on the unit's size. Over a 24-hour period, this wastes between 24Ah and 48Ah of your precious battery capacity for absolutely no reason. Always get into the habit of turning the inverter off at the switch as soon as you've finished charging your laptop or using 230V appliances.

Do I need solar panels if I drive my van every day?

Not necessarily. If your style of road trip involves driving every single day (for more than 1.5 to 2 hours), a correctly sized DC-DC charger (also known as a B2B or Battery-to-Battery charger) may be enough to fully replenish your leisure battery using the van's alternator. However, a solar array becomes essential if you plan to stay parked off-grid in one spot for several days at a time.

Why does Lithium provide more usable power than an AGM battery of the same capacity?

The secret lies in the permitted Depth of Discharge (DoD). A 100Ah lead-acid battery (AGM or Gel) should never be discharged below 50%, or you risk permanent cell damage and sulphation. This means a 100Ah AGM only gives you 50Ah of genuinely usable capacity. By contrast, a 100Ah Lithium (LiFePO4) battery can safely be discharged to 90% or even 100% depending on the BMS, giving you nearly twice the usable energy while weighing around a third of the weight.

How does cold British winter weather affect my off-grid power?

Winter is undeniably the toughest season for a campervan electrical system. Firstly, the sun is lower in the sky and the days are shorter, which can slash your solar yield by a factor of 3 or 4. Secondly, freezing temperatures temporarily reduce the chemical efficiency of batteries, and Lithium batteries will actively block taking a charge below 0°C to protect themselves (unless you invest in self-heating LiFePO4 models). Finally, winter is when your diesel heater (e.g., Autoterm, Webasto, or a Chinese diesel heater) will be running at full tilt, drawing constant fan and fuel pump power. If you are planning an all-season build, it is highly recommended to oversize your battery bank by at least 30%.

The Electrical Workshop