What size leisure battery do I need for a campervan?
Short answer: add up your daily energy use in watt-hours, multiply by the number of days you want to manage without any charging, and divide by the battery's usable depth of discharge (about 0.8 for lithium LiFePO4, 0.5 for lead-acid/AGM). Divide by 12 for amp-hours. Most weekend vans end up between 100 and 200 Ah of lithium. Vans used for working or long stays end up between 200 and 300 Ah.
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Step 1: work out your daily use (Wh)
For each appliance: watts × quantity × hours per day × duty cycle. Duty cycle matters most for fridges. A compressor fridge rated at 45 W doesn't run all day: the compressor cycles on and off, so 30–40% is a typical planning figure (more in hot weather).
| Appliance | Watts | Hours/day | Duty | Wh/day |
|---|---|---|---|---|
| 6 × LED lights | 3 each | 4 | 100% | 72 |
| Compressor fridge | 45 | 24 | 35% | 378 |
| 2 phones | 12 each | 2 | 100% | 48 |
| Roof fan | 20 | 4 | 100% | 80 |
| Water pump | 50 | 0.2 | 100% | 10 |
| Total | 588 Wh |
That's a typical "weekender" day: 588 Wh, or 49 Ah at 12 V.
Commonly missed: inverter standby (5–15 W, so up to 360 Wh a day if left on), 4G routers left on 24 hours, and diesel heaters (15–40 W average while running).
Step 2: decide how many days without charging
This is "days of autonomy": parked, not driving, no hook-up, and grey skies. If you move most days, one or two days is plenty. If you park up for a long weekend in winter, plan for three, or add more charging (it's usually cheaper and lighter than more battery).
Step 3: divide by usable depth of discharge
| Chemistry | Planning usable % | Notes |
|---|---|---|
| LiFePO4 (lithium) | 80% | Light, long life, fast charging. Needs a lithium charging profile; most can't be charged below 0 °C without built-in protection. |
| AGM / gel | 50% | Cheaper up front; heavier; deep discharges shorten its life. |
Weekender example: 588 Wh × 2 days ÷ 0.8 = 1,470 Wh ÷ 12 V = 122 Ah, so a 150 Ah lithium battery (or about 196 Ah of AGM: 588 × 2 ÷ 0.5 ÷ 12).
Three worked examples
| Van | Daily use | Days | Battery (LiFePO4) | Nearest common size |
|---|---|---|---|---|
| Weekender (lights, fridge, phones, fan, pump) | 588 Wh | 2 | 122 Ah | 150 Ah |
| Winter tourer (+ diesel heater 12 h, laptop 3 h) | 852 Wh | 2 | 178 Ah | 200 Ah |
| Remote worker (+ laptop 7 h, router 10 h) | 1,162 Wh | 2 | 242 Ah | 280 Ah |
All three are worked through in full (charging and cables included) in the 12V Van Electrics Guide (PDF, £8, English and French editions, sold on our Etsy shop).
Don't size the battery in isolation
A bigger battery only delays a flat battery if your charging can't keep up. Check your charging month by month: in London, 200 W of flat solar gives roughly 830 Wh a day in June but only about 90 Wh in December (PVGIS 2020–2023 data × 0.75 system factor). See Campervan solar in the UK, month by month.
FAQ
Is 100 Ah enough for a campervan? A 100 Ah lithium battery gives about 960 Wh usable. That covers the 588 Wh weekender day above for about a day and a half without charging, so it's enough if you drive or have solar most days.
Can I mix an old and a new battery? No. Only parallel identical batteries of the same age and chemistry, following the maker's instructions.
Lithium or AGM? For the same usable energy, lithium is roughly half the weight and lasts many more cycles. AGM costs less up front. Check prices at the time you buy.
This article is general planning information, not professional electrical advice. Always follow your battery and charger makers' instructions.