Power supply in motorhomes – components in focus – Part 4: Batteries

Batteries in motorhomes – energy storage for on the go

The leisure battery is the heart of your camper's electrical system. It determines whether your refrigerator runs continuously, your laptop stays charged, the heating works at night, and you can be self-sufficient for several days. But not all batteries are created equal: AGM, gel, or lithium – each technology has its own strengths and limitations. Then there are aspects like lifespan, charge cycles, wiring configuration, system voltage, and the possibility of converting to lithium batteries.

This article will tell you which battery is suitable for which type of trip, how much capacity you really need, and what you should pay attention to when planning.

Starter battery vs. leisure battery – what is the difference?

Campervans typically have two batteries with clearly distinct functions. The starter battery is responsible for reliably starting the engine. It must deliver very high currents in a short time and is not designed for frequent charging and discharging. The leisure battery – also called the auxiliary battery – handles the entire power supply for the living area. It stores electricity for lights, the refrigerator, the water pump, laptops, and all other appliances, and is designed to withstand numerous charging cycles and provide a continuous power supply.

Why the correct battery size is so important

The battery determines how long you can remain self-sufficient – ​​especially at night or in bad weather. Solar panels provide energy during the day, but in the evenings, at night, and on rainy days, your battery takes over the entire supply.

If the battery is too small , the following risks may occur:

• Functional limitations (e.g. refrigerator and heating)
• Faster deep discharge
• Reduced lifespan

If the battery is too large , you waste:

• Storage space
• Weight (important for 3.5 t!)
• budget

The goal is a balanced ratio between consumption, solar output, and battery capacity. And very importantly: even if you want to use solar power directly, you always need a battery. A solar system in a camper van simply won't work without one. While the solar charge controller ensures that fluctuations in the modules' output are compensated for and the battery is charged in a controlled manner, appliances cannot be operated directly from the charge controller. Solar modules don't deliver their energy constantly – they react instantly to every cloud, every shadow, and every movement of the vehicle. The charge controller only stabilizes this raw energy for the charging process. Only the battery provides a consistent voltage, thus enabling a reliable power supply for all devices. Without it, neither stable operation nor direct use of solar energy would be possible.

Battery types compared: AGM, Gel and Lithium

AGM batteries – proven and reliable

AGM batteries are robust, leak-proof, and relatively inexpensive. They handle higher currents well and are maintenance-free. However, you can only use about 50% of their capacity. Deep discharges are very damaging, and their weight is a disadvantage.

Suitable for: occasional use, weekend trips, small setups.

Gel batteries – a long-lasting classic

Gel batteries are also lead-acid batteries, but the gel electrolyte makes them even more stable and longer-lasting. They offer 500–1,200 cycles and very low self-discharge. However, they are sensitive to high charging currents and are just as heavy as AGM batteries.

Suitable for: regular use, moderate power requirements.

Lithium (LiFePO₄) – modern, efficient, lightweight

Lithium batteries offer maximum self-sufficiency: up to 90–100% usable capacity, extremely high cycle life (3,000–5,000+), half the weight, and stable voltage. They charge quickly, deliver high currents, and are ideal for modern campers – especially when using large inverters.

Suitable for: Vanlife, mobile working, e-bike use, long periods of self-sufficiency, demanding setups.

AGM, Gel & Lithium Overview

👉 Recommendation : In modern systems, lithium is almost always the best choice.

Lifespan & Deep Discharge

A battery's lifespan is measured in cycles – that is, how many times a battery can be fully discharged and then recharged. Each of these cycles corresponds to a complete charge and discharge cycle. Depending on the technology, batteries can go through a very different number of such cycles before their capacity noticeably decreases.

• AGM/Gel : approx. 300–1,200 cycles – they lose capacity faster, especially if they are regularly subjected to heavy discharges.
• Lithium (LiFePO₄) : 3,000–5,000+ cycles – they remain significantly more stable and efficient for years.

This high usable capacity results in a crucial advantage: A 100 Ah lithium battery often delivers the same amount of usable energy in everyday use as a 200 Ah AGM battery, because with lithium you can reliably access almost the entire capacity, while AGM or gel batteries only reliably provide about half of it. This explains why lithium systems are not only more durable in practice, but also significantly more efficient.

Series and parallel connection of multiple batteries

The choice between series or parallel connection determines whether you get more voltage or more capacity from your battery system. This directly affects which electrical devices you can power and how efficiently your system operates. It's important to understand how the connection type affects your entire electrical system.

Parallel connection – more capacity

• Voltage remains constant (e.g. 12 V)
• Capacity adds up (e.g. 2 × 100 Ah = 200 Ah)
• Perfect for campers who want to store more energy.

Series connection – higher voltage

• Voltage adds up (2 × 12 V = 24 V)
• Capacity remains the same
• Ideal for large, high-performance systems

Important : Only connect identical batteries – same technology, same capacity, same brand, same age.

12V or 24V – which system suits you best?

12V system :
Standard in campervans and compatible with almost all common devices. A 12V system operates with higher currents because less voltage is available for the same power output. This means : the cables need to be thicker and voltage drops occur more quickly – but the technology is widespread, spare parts are readily available, and many appliances such as refrigerators, lights, and chargers are designed to run directly on 12V.

24V system :
Here, twice as many volts are available, meaning that only half the current flows at the same power output. This reduces voltage losses and allows the use of thinner cables – a clear advantage in large installations, long cable runs, or with high-performance devices. 24V systems are primarily used in trucks or expedition vehicles.

The crucial difference between the two systems lies in the interplay of current, efficiency, and wiring complexity . A 12V system is compact, compatible, and ideal for typical camper applications. A 24V system demonstrates its strengths wherever high power is required – for example, with induction cooktops, powerful inverters, or extensive energy systems.

For most vans and motorhomes, 12V remains the best choice because the system is simple, reliable, and perfectly suited to common campervan technology. However, those planning a very power-intensive electrical system will clearly benefit from the advantages of a 24V setup.

If you would like to delve deeper: We have created a detailed blog article on 12V and 24V systems, in which all the differences are explained with graphics, examples and recommendations.

 

You can find the article here:
https://solarkontor.de/blogs/news/12v-oder-24v-welches-bordnetz-ist-das-richtige-fuer-mich

Converting from AGM to lithium – what you need to know

Switching to lithium batteries is NOT enough; simply replacing the battery is insufficient. Upgrading to lithium means your entire electrical system must be compatible with the new technology. Lithium batteries charge differently, deliver higher currents, allow for deeper discharges, and place significantly higher demands on charging technology and wiring. If even one component is incompatible, it can lead to malfunctions, unnecessary wear and tear, or even damage.

You need to make sure that:

• The charging booster is lithium-compatible – lithium requires a clear, precise charging voltage that a split charge relay cannot supply.
• The solar charge controller must have a lithium charging characteristic – only then will the battery be charged correctly and completely.
• The shore power charger supports lithium – older AGM/Gel chargers often have long absorption phases that can damage lithium.
• All cable cross-sections and fuses must be appropriately dimensioned – because lithium can provide high charging and discharging currents.
• A heating mat may be necessary for winter travel – many lithium batteries cannot be charged below 0°C. However, there are also special lithium batteries with an integrated heating mat that automatically enable charging at sub-zero temperatures and provide additional protection for the system.

Furthermore, the installation situation is worth considering: Lithium batteries are significantly lighter and more compact, and are therefore often installed in new locations within the vehicle. Temperature, ventilation, and accessibility must be suitable in these locations.

Your power consumption also plays a role: Do you use large inverters, induction cooktops, or do you regularly charge e-bikes? Then lithium shows its full potential – provided the rest of your electronics are also compatible.

Only when all components work together harmoniously can you benefit from the real advantages of a lithium battery: fast charging times, high usable capacity, long lifespan and maximum efficiency.

Which battery is suitable for whom?

Conclusion & Outlook

The battery is the central component of your power system. Whether AGM, gel, or lithium – the crucial factor is that it suits your consumption and travel habits. Lithium batteries currently offer the best combination of performance, lifespan, and weight and are clearly recommended for off-grid systems.

The next article will be about charging boosters and how you can reliably recharge energy while driving.