How many amp hours does your campervan or motorhome battery need? A step-by-step calculation

It’s the question we hear most at the counter from people travelling by campervan, motorhome or caravan around Málaga and the Costa del Sol: “How many amp hours should my leisure battery be?” There is no single figure that suits everyone, but there is a sum you can do in ten minutes. Here it is step by step, with a table of typical consumption and three worked examples.

The method: add up what you use in a day

Battery capacity is measured in amp hours (Ah), while your appliances state their consumption in watts (W). Getting from one to the other takes a single division: Ah = W ÷ 12 V × hours of use. A 12 W LED strip left on for 4 hours uses 12 ÷ 12 × 4 = 4 Ah.

If an appliance runs at 230 V through an inverter, the sum is the same, but add 10 to 15 % for the losses of the inverter itself.

Typical consumption by appliance

This table gives you a first estimate at 12 V. These are ballpark figures: the number that counts is the one on each appliance’s label or in its manual.

The fridge is nearly always the biggest consumer, and in the summer heat in Málaga the compressor runs for more hours. A heater draws considerably more during start-up, even if only for a few minutes.

Three worked examples

1. A weekend away with low consumption

A simple campervan, a portable coolbox without a compressor and the bare essentials: LED lights (15 W × 4 h = 5 Ah), water pump (2 Ah), two phones (3 Ah) and the roof fan now and then (20 W × 4 h = 7 Ah). Total: about 17 Ah a day.

2. A trip with a compressor fridge

A couple spending two weeks along the coast: compressor fridge (35 Ah), lights (5 Ah), pump (2 Ah), phones (3 Ah), laptop for two hours (10 Ah) and the roof fan at night (20 W × 6 h = 10 Ah). Total: about 65 Ah a day.

3. Living on board with an inverter

A motorhome used as a home, working remotely: fridge (40 Ah), lights (7 Ah), pump (2 Ah), heating or ventilation (15 Ah), phones (3 Ah), television (6 Ah), laptop for four hours through the inverter (22 Ah including losses) and a 1,000 W coffee machine for six minutes (about 10 Ah). Total: about 105 Ah a day.

From Ah used to Ah of battery

What you use is not what you need to buy. No battery should be drained completely, and how much you can draw depends on the technology:

• Lead-acid, EFB and AGM: count on around half of the capacity. Going below that as a habit shortens its life considerably.
• Lithium: you can use the great majority, around 80-90 %, and it weighs a good deal less too.

The full formula looks like this: battery Ah = daily Ah × days of autonomy ÷ usable share (0.5 for lead-acid and AGM; 0.85 for lithium). With two days without recharging, the three examples come out as follows:

Large capacities are achieved with one big battery or with two identical ones in parallel. And if you use an inverter, don’t look at the Ah alone: the battery also has to deliver the peak current it demands. Tell us the inverter’s power rating and we’ll check it.

How it is recharged and why that changes the sum

Days of autonomy are the days you spend with nothing going back in. If the battery is topped up every day, you need less capacity; if not, more. There are three routes:

• Alternator with a DC-DC charger: charges while you drive. A 30 A charger puts back about 30 Ah per hour on the road. On vehicles with a smart alternator it is practically essential.
• Solar panel: on the Costa del Sol it is your best ally. A 100 W panel can put back in the region of 25-30 Ah on a good sunny day; in winter or parked in the shade, a good deal less.
• Campsite hook-up: with the mains charger you get back to 100 % while you are plugged in.

If you drive every day or carry enough solar, you can size for a single day. If you stay put for a week without direct sun, for three or more. We explain it in leisure battery with a solar panel and in the guide to solar batteries.

Which battery to fit: Varta ranges for campervans in Málaga and the Costa del Sol

We are an Official Varta Distributor and these are the three ranges most often chosen for the living area:

• Varta Professional Dual Purpose AGM: sealed, maintenance-free and vibration-resistant. For example, the 95 Ah Varta LA95 or the 210 Ah Varta LA210.
• Varta Professional Dual Purpose EFB: enhanced lead-acid that works for both starting and leisure use. There is the 140 Ah Varta LED140 and the 240 Ah Varta LED240.
• Varta Professional Li-Ion Deep Cycle: lithium for anyone who needs a lot of usable Ah at low weight, such as the 100 Ah Varta LL100 or the 200 Ah Varta LL200.

You will find every capacity in the caravan batteries category. If you are torn between AGM and lithium, read the guide to lithium batteries first: when you change technology, the mains charger, the DC-DC charger and the solar controller must all be checked for compatibility.

For larger deep-cycle banks we also supply Trojan, Rolls and TAB, always by quotation: tell us voltage, capacity and dimensions and we’ll prepare it for you.

Compartment size and weight: check them before you buy

The sum can come out perfectly and the battery still not fit. Measure the length, width and height of the compartment, see which side the terminals sit on and leave room for the cables. For reference, the Varta LA95 measures 353 × 175 × 190 mm; the LA210, 518 × 276 × 242 mm.

Weight matters too, because it comes off the vehicle’s payload: the LA210 weighs 61.3 kg and the lithium LL200 weighs 30 kg for a similar capacity and far more usable Ah.

Ask for a quote with your sum done

Send us a WhatsApp or tell us by phone (+34 952 31 01 18) your daily Ah, how you recharge and the compartment dimensions, and we’ll tell you the right reference. We are at C/ La Orotava, 100, in Málaga: no appointment needed, we test your current battery free of charge and recycle the old one at no cost. We also deliver to campsites in Málaga and the Costa del Sol (ask about delivery times); delivery does not include fitting.

If you’d like to go over the basics first, there is the guide to caravan batteries and the one on leisure batteries for motorhomes and campervans.