How to Size & Wire a Campervan Electrical System (UK)

VanLife Beacon — builds each recommendation from a calculated energy budget and the manufacturer's own specs — every sourced figure links to its source, and anything that is a design convention rather than a measurement is flagged as such.

✓ Sourced on record

Most van electrical regret comes from buying parts before doing the maths. The right order is the opposite: work out your daily watt-hours, size the battery to cover them, then size every charging source to refill that battery. Here are the five blocks and how they fit together.

Methodology

Start with a real energy budget. Add up each load's watts × hours per day (fridge, lights, laptop, induction, water pump). That daily watt-hour figure sizes the battery; the battery sizes the chargers. Every number below is sized this way, and every component is a real UK-available unit checked in June 2026.

Daily watt-hour budget firstBattery sized to the budgetChargers sized to the battery

1 · The leisure battery — the heart

~80% (sizing) usable capacity · LiFePO4

~50% usable capacity · lead-acid

0 °C cold-charging limit

Your daily watt-hour budget sets the battery. In LiFePO4 you can use nearly the full rated capacity, so a 105Ah (≈1,280Wh) Fogstar Drift covers a modest day; heavy all-electric builds stack several. Lead-acid would need roughly double the rated capacity for the same usable energy — which is why new builds go lithium.

	Usable	Cycles	Cold charge
LiFePO4	~80% (sizing)	3,500+	needs heater
AGM lead-acid	~50%	~500	tolerant

Cold-charging limit Below freezing, LiFePO4 must not take charge without a self-heating cell or a battery kept in the warm habitation space — charging a frozen cell damages it permanently.

2 · Charging while you drive — DC-DC, not a relay

A modern Euro 6 van has a smart alternator whose voltage varies, so an old split charge relay barely charges a lithium battery. Fit a DC-DC (battery-to-battery) charger instead — a Sterling Power BB1230 (30A) or Victron Orion XS (50A, 700W) pulls a steady, correctly-staged current. Size it in amps: bigger refills faster but loads the alternator more.

3 · Solar — the daily top-up

Roof panels feed an MPPT charge controller, which extracts more from the array than a cheap PWM unit, especially in dim British light. Size the controller to your panel wattage and charge current. Solar carries three seasons; British winter days are short, so plan a fallback.

4 · The inverter — making 230V

To run mains appliances you need a pure sine wave inverter sized by continuous watts and surge. Pure sine is non-negotiable for laptops, induction and anything with a motor. Many builders skip a separate inverter entirely by using an all-in-one power station that already contains one.

5 · Hook-up and the gauge

Electric hook-up (EHU) is the winter and emergency fallback: a 230V campsite feed through a blue 16A lead and an RCD. Finally, fit a battery monitor with a shunt — it counts every amp in and out and is the only honest state-of-charge reading on LiFePO4. Without it you run blind.

Key takeaways

Size from daily watt-hours first; the battery and chargers follow.
LiFePO4 gives nearly full usable capacity — lead-acid needs ~double.
Euro 6 vans need a DC-DC charger, not a split charge relay.
An MPPT controller beats PWM in low light; pure sine inverter for sensitive loads.
A shunt battery monitor is the one gauge you can trust.

How to size and wire a campervan electrical system

Methodology

1 · The leisure battery — the heart

2 · Charging while you drive — DC-DC, not a relay

3 · Solar — the daily top-up

4 · The inverter — making 230V

5 · Hook-up and the gauge

Key takeaways

Used in

Sources