Leisure battery and solar panel in a campervan or motorhome: how to match them

If you have, or are about to fit, a solar panel on your campervan, motorhome or caravan, the leisure battery is half the system: the panel produces, but the battery is what stores the energy for the night. In Málaga and on the Costa del Sol we have an advantage, because the sun shines for most of the year, and that allows tighter battery banks than in northern Europe. Here is how to match panel, charge controller and battery so the system works and the battery lasts.

The basic layout: from the panel to the loads

Every solar set-up in a leisure vehicle, large or small, follows the same path.

The panel is never wired straight to the battery: it always goes through the controller, which cuts off when the battery is full and stops it discharging back into the panel at night.

The starter battery stays separate. It belongs to the engine, the alternator charges it and it should not feed the living area, because if you drain it you will not start. Some controllers have a second output that keeps it topped up while the vehicle is parked. If you are not sure which is which, we explain it in caravan batteries.

PWM or MPPT charge controller

• PWM: simple and inexpensive. It pulls the panel voltage down to the battery voltage and the surplus is lost. Fine for a small panel that only keeps the battery topped up.
• MPPT: finds the point at which the panel delivers most and turns the surplus voltage into charging current. It gets more out of the same panel, especially under cloud or with higher-voltage panels.

The charging profile is what matters

More important than the acronym is that the controller has the charging profile for your battery technology. Each one needs its own voltages: flooded lead-acid accepts equalisation, AGM does not; lead-acid benefits from temperature compensation, lithium does not want it and has no use for a long float stage. With the wrong profile the battery is left half charged or stressed on every cycle.

Which leisure battery to pair with a solar panel

Dual-purpose or deep-cycle AGM

Sealed, maintenance-free and spill-proof, and it copes well with vibration. It is the balanced choice for most campervans. To make it last, do not routinely take it below half its capacity.

Dual-purpose EFB

Enhanced flooded lead-acid, built to cycle more than an ordinary battery. It suits moderate use and anyone who wants a robust battery that can also crank an engine.

LiFePO4 lithium

You can use nearly all of the capacity, it weighs around half as much and it accepts far more cycles. It has a BMS that protects it. In return it needs a controller and chargers with a lithium profile. The full reasoning, written for boats but just as valid here, is in lithium on board.

Flooded traction batteries, for fixed installations

Flooded lead-acid traction batteries are made for deep discharges every day. They need the water level checked and a ventilated compartment, so they make sense in a static caravan on a pitch or in an off-grid installation, not under the seat of a campervan.

How much panel for how much battery

There is no magic figure, but there is a rule: on a normal day, the panel has to give back to the battery what you have used since the day before. If it produces less, you start each morning a little lower and the battery ends up living half charged, which is what harms lead-acid most.

The battery, for its part, is sized to get you through the night and the bad days. This is where Málaga helps: on the Costa del Sol it is unusual to get many sunless days in a row, so you do not need as much reserve as someone touring northern Europe. Watch out in winter: the sun is lower, the days are shorter and a panel lying flat on the roof yields less.

• Weekend trips: LED lights, water pump, phones and a compressor fridge. One roof panel and a mid-sized AGM or EFB battery are usually enough; the alternator makes up the rest on the road.
• Living on board or working remotely: inverter, laptop, coffee machine and a fridge that never stops. You need several panels, an MPPT controller and a larger bank; this is where lithium pays off in usable capacity and weight.

The figures for your own case are worked through step by step in how many Ah your campervan needs.

Five common mistakes

1. Using a starter battery as a leisure battery. It is made to deliver a lot of current for a few seconds, not to be emptied every night. It lasts very little.
2. A controller with no lithium profile. The battery never fills or the BMS disconnects it, and it looks as if ‘lithium doesn’t work’.
3. Thin or overlong cables. The voltage drop misleads the controller and the charge falls short. Use the right cross-section and a fuse close to the battery.
4. Panels in the shade. A rooflight, an aerial or a tree covering one corner can collapse the output of the whole panel.
5. Mixing batteries of different age, capacity or type. The old one drags the new one down. In a bank, all identical and all replaced together.

The heat in Málaga: where to put the battery

The panel wants sun; the battery does not. Inside a closed vehicle in the summer sun the temperature gets very high, and in heat any battery ages sooner, lead-acid or lithium.

• Put it in the coolest spot: low down, away from the engine, the heater and the inverter.
• Let the compartment breathe. Even a sealed AGM has safety valves; flooded lead-acid needs venting to the outside.
• With lead-acid, use the controller’s temperature sensor if it has one, and do not leave the battery discharged while the vehicle is in storage.

The leisure batteries we stock in Málaga

At Málaga Baterías we are an Official Varta Distributor. For leisure use with solar we work with the Varta Professional Dual Purpose AGM and EFB and Varta Professional Li-Ion Deep Cycle ranges. In the online shop they are listed as marine because they share the range with boats:

• Varta LA95 12V 95Ah 850A: dual-purpose AGM in a size very common in campervans.
• Varta LA105 12V 105Ah 950A: AGM with a little more capacity in a longer case.
• Varta LED95 12V 95Ah 850A: dual-purpose EFB for moderate use.
• Varta LED140 12V 140Ah 800A: EFB for motorhomes with a large battery bay.
• Varta LL100 12.8V 100Ah: deep-cycle lithium, about half the weight of an AGM of similar capacity.
• Varta LL150 12.8V 150Ah: lithium with more reserve for those who live on board.

You will find the rest in the caravan batteries category. In deep-cycle and traction we also supply Trojan, Rolls and TAB on quotation.

We sell and deliver the battery; fitting panels and controllers is a job for your installer or for you. We deliver in Málaga and along the Costa del Sol, campsites included: ask us for the delivery time. Tell us which panel and controller you have, what you run and the size of the battery bay, and ask for a quote on WhatsApp or on +34 952 31 01 18. We take back the used battery and recycle it at no cost.