What Size Leisure Battery Do I Need? (UK 2026)

By the Leisure Cell editorial team · Updated 2026 · How we test & score

Buy too small and you run out of power; buy needlessly big and you waste money and weight. Sizing a leisure battery comes down to your daily consumption and the usable-capacity rule. Here's how to get it right.

Work out your daily consumption

List everything you'll run off the battery and estimate the amp-hours each uses per day: current draw in amps multiplied by hours of use. Lights and charging are modest; a compressor fridge, a water pump running often, or an inverter powering mains appliances add up fast. Total these to get your daily amp-hour consumption. This is the single most important number, and being honest about big loads is what stops you under-sizing.

Apply the usable-capacity rule

Your battery's rated Ah is not all usable. For flooded, AGM and gel, only draw around half before recharging, or you shorten its life - so you need roughly double your daily consumption in rated capacity. For lithium, you can use most of the rating, so you need close to your daily consumption plus a margin. This rule is why lithium of the same nominal size goes much further, and why sizing on rated Ah alone misleads.

Add a margin and check the fit

Add headroom for cloudy days with little solar, longer stops between charges, and colder weather when you use more. A day or two of reserve is sensible. Then check the resulting battery physically fits your box and its weight suits your vehicle. If the required lead-acid capacity becomes huge and heavy, that's often the point where lithium - lighter and giving more usable capacity - makes practical sense.

Our top picks

Frequently asked questions

What size leisure battery do I need for a weekend?

For a weekend of modest use - lights, phone charging, a water pump, maybe a small fridge - with a recharge in between, many people manage on a single 100Ah lead-acid battery (around 50Ah usable) or a smaller lithium. If you run a compressor fridge continuously or use an inverter, you'll need more usable capacity. Work out your daily amp-hours and double it for lead-acid to size it properly.

How do I calculate what leisure battery I need?

Add up each device's current draw in amps times the hours you use it, to get your daily amp-hour consumption. Then, for lead-acid or AGM, double it (since only about half is usable) and add a margin - that's your rated capacity. For lithium, size to a little above your daily consumption since most is usable. Round up to a standard size that fits your battery box, and add reserve for cloudy days or longer stops.

Bottom line

Our top pick is the Photonic Universe Gel (our score 9.6/10) - A practical leisure battery (gel, 100Ah) for off-grid and leisure power..

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