Choosing Campervan Leisure Batteries for Your Build

A fridge that cuts out overnight, dim lights after one evening, or a voltage drop when the water pump starts are usually not appliance faults. They are signs that the campervan leisure batteries, charging equipment and expected power use have not been matched properly. Get the electrical system right early in the build and it will support the rest of the conversion: refrigeration, lighting, USB charging, water, heating controls and occasional mains-free working.

A leisure battery is not simply a second vehicle battery. It is designed to supply a steady amount of power over a longer period and to be recharged repeatedly. The correct type and capacity depend on how you use the van, where it is parked, and how you plan to recharge it.

Start with the loads, not the battery

The most common mistake is choosing a battery by its advertised amp-hour figure before calculating what the van will use. Start with the appliances that will run away from hook-up. A compressor fridge is normally the largest regular load, followed by a diesel heater, water pump, lighting, charging points, roof vent and any inverter-fed equipment.

For each item, multiply its current draw in amps by the number of hours it is expected to run each day. That gives a usable estimate in amp-hours (Ah). A 4A fridge compressor that runs for six hours across a warm day uses around 24Ah. Four LED lights drawing a combined 1A for five hours use 5Ah. A diesel heater may use relatively little once running, but its start-up cycle can draw considerably more.

Allow for real conditions. Fridges work harder in a hot van, batteries lose available capacity in cold weather, and a weekend off-grid is different from a week parked in a shaded campsite. Add a sensible margin rather than sizing the system to a best-case calculation.

Usable capacity matters more than the headline figure

A 100Ah lead-acid battery should not routinely be taken close to empty. In practical terms, planning around roughly 50 per cent discharge helps preserve its service life. A 100Ah lithium iron phosphate battery, commonly called LiFePO4, can generally provide substantially more of its rated capacity without the same penalty, subject to the battery manufacturer's limits and battery management system.

That is why a smaller lithium battery can sometimes outperform a larger AGM unit in daily use. It does not mean lithium is automatically the right choice. Purchase cost, low-temperature charging, charging equipment and installation position all need consideration.

Campervan leisure batteries: choosing the chemistry

Lead-acid batteries remain a workable option for basic, lower-cost builds, particularly where the van spends much of its time on electric hook-up. Flooded lead-acid batteries are generally the least expensive, but they must remain upright and require suitable ventilation because they can release gas during charging. They are rarely the first choice for an enclosed living area.

AGM batteries are sealed lead-acid units with better tolerance for repeated cycling than a standard starter battery. They suit many weekend vans and are straightforward to source. Their drawbacks are weight, slower charging compared with lithium and reduced usable capacity. Gel batteries are also sealed and cycle-capable, but need an accurately matched charging profile and can be less forgiving of incorrect charging voltages.

LiFePO4 batteries are lighter, charge quickly and offer high usable capacity. For regular off-grid use, especially with a compressor fridge and solar charging, they are often the practical long-term option. However, lithium batteries need a compatible charger, DC-DC charger and solar controller. They should not be charged below freezing unless the battery includes low-temperature charge protection or integrated heating.

A built-in battery management system is essential. It protects lithium cells against over-charge, over-discharge, excessive current and, on suitable models, low-temperature charging. It is protection, not a substitute for correct cable sizing, fusing and charger settings.

Match capacity to how the van is used

For occasional overnight stops with LED lighting, mobile phone charging and a small water pump, a modest battery bank may be enough. Add a compressor fridge and regular off-grid weekends, and 100Ah of lithium or a larger lead-acid bank becomes more realistic. Vans used for extended touring, remote working or winter trips may need 200Ah or more, backed by reliable charging.

High-wattage appliances change the calculation quickly. A 1,000W inverter can draw more than 80A from a 12V battery before allowing for losses. A hair dryer, kettle, air fryer or electric heater may run briefly, but they demand substantial battery capacity, heavy cabling and a properly designed inverter installation. For most compact campervan systems, gas cooking or campsite hook-up is more practical than building around large electric heating loads.

Physical dimensions matter as well. Measure the intended battery location before ordering. Check height, terminal orientation, service access, cable routing and how the unit will be restrained. A heavy battery must be securely fixed so it cannot move under braking or cornering. Keep terminals protected from accidental contact with metal furniture, tools or stored equipment.

Build charging around the battery bank

Battery capacity only helps if it can be replaced. Most campervans use a combination of alternator charging, solar and mains hook-up charging. Each source does a different job.

A modern vehicle should normally use a DC-DC charger between the starter battery and leisure battery. Smart alternators can reduce output once the vehicle battery is charged, so an old-style split-charge relay may not provide a reliable charge. A DC-DC charger takes a controlled input and delivers the correct multi-stage charge profile for the leisure battery. It also limits demand on the vehicle charging system.

Solar is useful when the van is parked, particularly from spring to early autumn. Panel output varies with season, cloud, angle, shading and cleanliness. Treat quoted panel wattage as a favourable-condition figure, not a daily guarantee. An MPPT solar controller is generally worth using because it makes better use of available panel voltage, particularly in less-than-perfect light.

A mains battery charger is needed for hook-up and for charging at home. Set it to the battery manufacturer's stated chemistry and voltage requirements. Do not assume an older charger is suitable for lithium simply because it can produce 14.4V. Check its charging stages, float behaviour and whether the lithium battery maker approves that profile.

Cable size, fuses and isolation are part of the battery system

A quality battery cannot compensate for undersized cable or missing protection. DC current is high at 12V, especially around inverters, DC-DC chargers and battery links. Cable size must be selected for the maximum current and the total cable run, including both positive and negative paths. Longer runs create more voltage drop, which can make appliances perform poorly even when the battery is charged.

Fit a fuse or circuit breaker close to the positive battery terminal for every cable leaving the battery. The fuse protects the cable, so its rating must suit the cable's current capacity and the expected load. A battery isolator is also useful for maintenance, fault finding and storage, but it does not replace correct fusing.

Use properly crimped terminals, heat-shrink where appropriate and secure cable runs with suitable clips or conduit. Avoid running unfused positive cables through sharp metal openings. Where a cable passes through bodywork or furniture, fit grommets and protect it from abrasion. Keep a clear wiring diagram with fuse ratings and cable sizes - future troubleshooting is much easier when the build is documented.

Do not ignore monitoring

Voltage alone is a rough guide, particularly with lithium, where voltage can remain fairly stable through much of the discharge cycle. A shunt-based battery monitor measures current moving in and out of the battery bank and gives a more useful state-of-charge reading. It also shows whether the fridge, inverter or charging source is behaving as expected.

This is valuable during the first few trips. Monitor a normal evening, an overnight stop and a full day without driving. Real figures will show whether the battery bank is sufficient or whether reducing a load, adding solar or increasing charging capacity would make better sense.

For a dependable installation, specify the battery alongside the fridge, heating, solar, DC-DC charger, mains charger and cable routes rather than treating it as the last item to fit. A well-sized system is quieter in use than a generator, more useful than a large battery with no way to recharge it, and far easier to live with once the van is finished.