Every off-grid conversation ends up at the same ledger. Your leisure battery holds a fixed number of amp-hours. Everything you switch on withdraws from it. The van doesn't care about your plans. It cares whether the withdrawals beat the deposits, and on most vans they do sooner than the brochure implied.
Count in amp-hours, not hope
Start with what you have. A 100Ah lead-acid or AGM battery gives you roughly 50Ah of usable capacity, because discharging below half wrecks its lifespan. A 100Ah lithium battery gives you 80–90Ah usable from the same label. That difference is the entire lithium argument, and as of 2026 the price gap has narrowed enough to make it mainstream: reputable budget UK lithium brands sit around £200–400 for 100Ah, where the premium names still want £700 and up. Whatever you run, the usable number is your daily allowance. Everything below draws against it.
The fridge is the main event
A 12V compressor fridge draws 2–4 amps while the compressor runs, and it runs 20–50% of the time depending on how warm the van is and how often the door opens. Over 24 hours that's typically 30–50Ah. Read against the 50Ah usable in a standard lead-acid setup, that means the fridge alone can empty your allowance in a warm day. Nothing else comes close. LED lights cost a couple of amp-hours an evening, two phones maybe 5–8Ah, a diesel heater's fan and pump perhaps 10–15Ah overnight in winter. The laptop-and-TV tier adds up, but the fridge is the tide everything else floats on. Owners with three-way absorption fridges dodge this entirely by running on gas off-grid, which is why that older technology refuses to die.
Ways to put it back
Hookup is the boring answer and the best one where it exists: a UK campsite pitch fee nearly always includes 16A of mains, your battery charger does the work while you sleep, and the fridge problem disappears. Off-grid, you have three realistic deposits. Solar is the favourite, but the panel's label is a summer number: a 100W panel might return 25–30Ah on a bright June day in Britain and 5Ah on a grey one in December. Size for the season you'll actually travel in, not the sticker.
The alternator is the deposit most owners underuse. A 30A B2B charger turns a two-hour drive into 50–60Ah, which on tour means normal driving days keep the ledger balanced without you thinking about it. It only fails you when you stop moving. Four nights parked by a Pembrokeshire beach is exactly when the B2B contributes nothing and solar earns its keep.
Portable power stations are the no-installation route: charge the box at home or on hookup, run your kit from its sockets, and accept that as of 2026 a usable 1kWh unit costs a few hundred pounds: more per stored watt-hour than a lithium leisure battery, bought back in convenience and zero wiring. For a weekender van or a rented motorhome they make real sense. For full-time off-grid they're the expensive way to do what a proper battery and B2B do better.
Inverters: the quiet thief
An inverter turns 12V into 230V and takes a cut both ways. Conversion losses run 10–15%, and most inverters draw half an amp to an amp just sitting switched on, which is 12–24Ah a day for the privilege of a glowing standby light. The kettle sum is the one to memorise: a 3kW domestic kettle wants roughly 250 amps at 12V. That's a design error: boil water on gas, charge laptops on 12V USB-C where you can, and save the inverter for the things that genuinely need mains. Then switch it off at the panel.
Winter is a different sport
Summer flatters every setup. In winter the solar deposit collapses to near nothing, the heater adds a nightly withdrawal, and the battery itself weakens: lead-acid loses usable capacity in the cold, and most lithium batteries refuse to charge below freezing unless they have a built-in heater, which is worth paying for if you tour in January. The honest winter plan for an ordinary van is hookup most nights and the alternator between them, with off-grid stops as the exception. That's reading the ledger.
Two Octobers of logged levels told one van's true story: leisure battery down 18% overnight in summer, 31% in autumn with the heater running. Not a guess off a flickering voltmeter: arrival and departure readings across forty-odd stops. That number is what finally settled the solar-versus-B2B argument, because it showed drive days already covered the drain.
Once you know your real overnight number, sizing the system stops being forum folklore and becomes shopping. The panels, batteries, B2B chargers and power stations we'd fit are on the electrical and power gear page.
Getting that number is the easy part: log the leisure battery level on arrival and departure and the pattern shows up inside a fortnight. If the van itself is electric, the vehicle's charge is tracked separately from the habitation side, which keeps the two sums apart: running an electric campervan. And the other half of the same discipline is water and waste on the road.
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Find your true overnight drain
Log leisure battery and power station levels on arrival and departure in Stops & Stays and the pattern shows up within a week. Ten stops free. No ties.
