At the centre of every campervan, caravan or motorhome is the electrical system. From lighting and sockets to pumps, fridges, heating and cooling, everything needs a reliable source of power and a way to replace the energy you use.
This guide covers the basics of:
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The leisure battery that stores your power
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How power is supplied around the vehicle
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The three main ways to charge the leisure battery: solar, charging while driving and mains hook-up
Campervan Electrics: Charging
Mains Charging
Solar Charging
Charging While Driving
Hooking up to mains is a great way to bring 240V in for your mains appliances, while also charging your leisure battery through a mains charger.
A solar system is made up of two parts: the solar panels that capture daylight, and a solar regulator (controller) that turns what they produce into a safe, steady charge for your battery.
A DC-DC charger draws from your vehicle’s alternator to charge the leisure battery as you drive. It means you can keep your must-have appliances running on the move, and arrive with your system topped up.
Key points:
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Reliable and consistent: it doesn’t depend on the weather or on driving.
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The fastest, steadiest way to charge; it’ll happily refill the battery overnight.
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Powers 240V appliances directly while you’re plugged in.
Key points:
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Free, quiet and maintenance-free once it’s fitted.
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Can top the battery up throughout the day while usable daylight is available.
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No moving parts and nothing to switch on, it just works in the background.
Key points:
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Charges automatically whenever you’re on the move.
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Puts a charge in without relying on a hook-up, or on solar and the weather.
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Gives the battery a correct, controlled charge. Important for lithium and modern smart alternators.
Be aware:
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You need a hook-up point, so it’s no help when you’re truly off-grid.
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Sites often charge for electricity (sometimes metered), and you’ll need the right hook-up lead.
Be aware:
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Output rises and falls with the time of day, weather, seasons and shade.
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The panels need a regulator sized to suit them. Without the right one, they won’t charge the battery properly.
Be aware:
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It only charges while you’re driving, so short hops won’t put much back.
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Needs the right cabling and a DC-DC unit matched to your alternator.
Campervan Electrics: Leisure Batteries
The leisure battery powers the equipment on board your campervan, caravan or motorhome. What you want to run, how long you want to use it for, and where you plan to use the vehicle will help determine not only the right battery type and capacity, but also the best way to recharge it.
Three common battery types
Wet Lead
AGM (Absorbent Glass Mat)
Lithium (LiFePO₄)
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The most basic option.
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Still found in older systems and budget setups.
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Heavier and generally offers less usable capacity than newer batteries.
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Largely superseded by AGM for leisure use.
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Sealed and maintenance-free.
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Works with the vast majority of chargers.
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Reliable and well-proven.
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Still the most common battery type in caravans and motorhomes.
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The modern standard for serious builds.
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Lighter, longer-lasting and far more usable capacity.
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Requires lithium-compatible charging (mains charger, DC-DC charger and solar regulator).
What is depth of discharge?
Depth of discharge (DoD) is how much of a battery’s power is actually usable.
100Ah lead-acid / AGM
100Ah lithium
≈ 50Ah usable
≈ 80–90Ah usable
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DoD around 50%.
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50Ah of usable capacity from a 100Ah battery.
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Keep within 50% to preserve battery life.
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DoD 80–90% (based on manufacturer).
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Significantly more usable energy.
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Higher cycle life.
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Two batteries with the same Ah rating can provide very different amounts of usable energy. It’s the usable capacity that counts.
How much capacity do you need?
Start with what you want to power and how long you use it for. Consider items such as the fridge, heater, pump, lights and chargers, including which run continuously and which are only used occasionally.
Battery capacity
Typical starting point
100–120Ah
Weekend use, smaller vans, modest daily loads.
Around 200Ah
Greater off-grid capability, with a fridge and general use.
300Ah+
Longer trips, extended off-grid stays, or regular inverter use.
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These are general guides. A battery is only a tank, and how long it lasts depends as much on how you refill it as on the size of the battery.
Is lithium worth it?
Lithium batteries cost more upfront, but they offer significant advantages:
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More usable capacity for the same Ah rating (roughly double compared to lead-acid).
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Generally lighter and takes up less space.
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Can offer a significantly longer cycle life.
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Ideal for customers who regularly travel off-grid or use higher electrical loads.
Campervan Electrics: Getting It Right
Running Mains Appliances in Your Vehicle
There are two main ways to use 230V mains appliances in a campervan, caravan or motorhome.
Mains hook-up
When connected to a mains supply, you can:
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Run 230V appliances from the hook-up connection.
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Charge the leisure battery with a mains battery charger.
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Continue to run 12V appliances (lights, pumps, fridges etc.) from the battery while it is being charged.
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Mains hook-up provides a convenient way to run mains appliances and recharge the leisure battery at the same time.
Inverters
An inverter converts 12V DC from the leisure battery into 230V AC, allowing you to use mains appliances away from hook-up.
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Choose an inverter based on the appliance’s running wattage and any start-up (surge) requirement.
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Larger inverters require a larger battery bank.
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Lithium batteries are often better suited to high inverter loads as they can supply high currents efficiently.
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Key point: A 2,000W inverter does not create 2,000W of power. The energy still comes from the leisure battery.
Cable Size, Fusing and Voltage Drop
Correct cable sizing and fusing are essential in a 12V system. Low voltage and high current mean the right cable size is needed to get power from the battery to the appliance.
Why cable size matters
Every appliance requires a certain voltage and current to operate correctly. If the cable is too small for the current being drawn or the distance it has to travel, resistance in the cable causes voltage drop.
Voltage drop can result in:
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Poor appliance performance
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Fridges or heaters cutting out
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Pumps running slowly
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Inverters alarming or shutting down
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Cables becoming warm or overheating
Choosing the right cable size
Cable size should be based on:
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Current draw (amps)
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Cable length (distance)
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Acceptable voltage drop
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The longer the cable run and the higher the current, the larger the cable needs to be to keep voltage drop to a minimum.
Fusing
Each circuit should be correctly fused. The fuse protects the cable and circuit if excessive current flows.
Key points:
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Use the correct cable size for the load and cable length.
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Keep voltage drop as low as possible.
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Fit the correct fuse for the circuit.
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Ensure all connections are secure and corrosion-free.
Troubleshooting
If an appliance is not performing as it should, follow these steps to identify whether the issue is with the battery, the wiring or the appliance itself.
1
Check the battery first
Measure directly across the battery terminals with nothing running. A fully charged battery will typically read:
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Lead-acid / AGM: around 12.7V
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Lithium (LiFePO₄): around 13.2–13.4V
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These are general guides. Lithium has a very flat voltage curve, so voltage alone is not a reliable indication of state of charge.
2
Measure under load
Switch the appliance on and compare the voltage at the battery and at the appliance.
Example readings (12V fridge)
Battery at rest (no load)
12.7V
Battery with appliance running
12.4V
At appliance (switched off)
12.6V
At appliance (running)
11.8V
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If the voltage remains healthy at the battery but drops significantly at the appliance, the problem is likely somewhere in the supply circuit.
3
Isolate the appliance
If an appliance (for example a fridge) is underperforming, remove it from the vehicle circuit and test it close to the battery using a short, correctly sized and fused cable. This bypasses the existing wiring, fuse holders, connections and distribution system.
This helps you identify if:
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The appliance works correctly → the issue is likely in the original wiring, connections or fuses.
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The appliance still performs poorly → the appliance itself, or the battery, may require further investigation.
Common causes of problems
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Undersized cable
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Excessive cable length
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Loose or poor connections
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Corroded terminals
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Blown or incorrect fuses
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Poor earth / negative
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Voltage drop in wiring
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Appliance overloaded
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Voltage dropping under load
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Ageing or failing battery
Battery health
Batteries have a limited number of charge and discharge cycles. As they age, their usable capacity reduces and they may drop significantly in voltage when a load is applied, even if they show a normal voltage with no load.
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