What battery does a camper need: AGM, GEL or lithium and how many Ah?

Choosing an auxiliary battery for a camper seems simple until terms such as AGM, GEL, lithium, LiFePO4, Ah, Wh, BMS, alternator charging and depth of discharge start appearing.

The truth is that there is no perfect battery for every camper. The right choice depends on how much power you use, how long you want to stay off-grid, how you recharge, and how much space and budget you have.

In this guide, we compare AGM, GEL and lithium batteries and, above all, show you how to calculate how many Ah you really need. How many Ah do you really need?.

First things first: what does Ah mean on a battery?

Amp-hours (Ah) indicate a battery's electrical capacity. In a 12 V system, a 100 Ah battery stores approximately:

12 V × 100 Ah = 1,200 Wh

That is roughly 1.2 kWh of theoretical energy.

But that does not mean you can always use 100% of that energy. The amount you can actually use depends on the battery technology, its condition, temperature and how it is used.

AGM, GEL or lithium: quick comparison

Features	AGM	Gel	LiFePO4 lithium
Initial cost	Low/medium	Medium	High
Weight	High	High	Low
Usable energy	Medium	Medium	High
Charging speed	Medium	Medium / slow	High if the system is compatible
Service life	Medium	Medium / high	High
Needs a BMS	No	No	Yes
Best for	Occasional use and a limited budget	Moderate discharges and controlled charging	Frequent use, off-grid autonomy and weight savings

What is an AGM battery?

AGM stands for Absorbent Glass Mat. It is a sealed lead-acid battery in which the electrolyte is absorbed into a fibreglass mat.

For years, it has been one of the most commonly used auxiliary batteries in campers and motorhomes because it is relatively affordable, widely available and compatible with many existing electrical systems.

Advantages of an AGM battery

• Lower initial cost than lithium.
• Well-established and widely used technology.
• Available in many capacities and sizes.
• Can work well in a camper used occasionally.
• Does not require an external BMS like a lithium battery.

Disadvantages of an AGM battery

• It is relatively heavy.
• It should not be deeply discharged on a regular basis.
• The energy you can realistically use is much lower than its nominal capacity if you want to preserve its lifespan.
• It usually provides fewer charge cycles than a good LiFePO4 battery.
• It can take longer to reach a full charge.

That is why comparing a 100 Ah AGM battery with a 100 Ah lithium battery based only on the number printed on the label can be misleading.

What is a GEL battery?

GEL batteries are also lead-acid batteries. In this case, the electrolyte has a gel-like consistency.

They can work well in leisure electrical systems and cope well with moderate discharge cycles, but they need charging parameters suited to their specific characteristics.

Advantages of a GEL battery

• Good cycle durability when used correctly.
• Sealed and low-maintenance battery.
• Can be a good option in systems already designed for GEL batteries.

Disadvantages of a GEL battery

• Heavy weight.
• Usually more expensive than an equivalent AGM battery.
• Requires the correct charging parameters to be respected.
• Does not offer the same weight-to-usable-energy ratio as lithium.

What is a LiFePO4 lithium battery?

When we talk about “lithium” batteries in camper electrical systems, we usually mean LiFePO4, or lithium iron phosphate batteries.

Their main advantage is that you can use a much larger proportion of their capacity without the same drawbacks as lead-acid batteries. They are also much lighter and can charge faster when the rest of the system is designed for it.

Advantages of LiFePO4 lithium

• Much lower weight for a similar capacity.
• More usable energy.
• More charge cycles under suitable conditions.
• More stable voltage throughout most of the discharge cycle.
• Can accept high charging currents if the battery and system allow it.
• Very attractive for frequent travellers.

Disadvantages of lithium

• Higher initial cost.
• Requires a BMS.
• May require changes to the mains charger, DC-DC charger, solar controller or other components.
• Not all lithium batteries can be charged below freezing.
• A poorly designed electrical system can prevent you from taking full advantage of its benefits.

What is a BMS and why does it matter?

The BMS, or Battery Management System, is the electronic system that protects and manages a lithium battery.

• Monitors cell voltage.
• Protects against overcharging.
• Protects against excessive discharge.
• Limits currents outside safe operating ranges.
• Can protect against unsuitable temperatures.
• Some models allow Bluetooth monitoring.

Not all batteries with the same capacity use the same BMS. If you plan to use a powerful inverter, for example, check the battery's maximum continuous discharge current.

So, how many Ah does a camper need?

Do not start with the battery. Start with your power consumption.

Make a list of everything you will use and estimate how much energy each device consumes per day.

Device	Example daily consumption
LED lights	50 Wh
Phones and small devices	80 Wh
Water pump	20 Wh
Compressor fridge	350 Wh
Laptop	120 Wh
Diesel heater: electronics/fan	150 Wh
Example total	770 Wh/day

The figures in the table are only examples. The actual consumption of a fridge, heater or laptop can vary greatly depending on the model, ambient temperature and how long it is used.

How to convert Wh to Ah

In a nominal 12 V system, you can make a simple estimate:

Ah ≈ Wh ÷ 12

Using the 770 Wh daily consumption from the example:

770 Wh ÷ 12 V ≈ 64 Ah per day

This means you need roughly 64 Ah of 12 V-equivalent energy per day before allowing for losses and safety margins.

Example: runtime with a 100 Ah lithium battery

A 100 Ah LiFePO4 battery at 12.8 V stores around 1,280 Wh nominally.

If your daily consumption is around 770 Wh, a battery of this size could theoretically provide roughly a day and a half of power without recharging.

In practice, you should allow some margin for losses, variations in consumption and to avoid relying on fully draining the battery every day.

Example: runtime with a 100 Ah AGM battery

A 100 Ah AGM battery also has a nominal capacity of around 1,200 Wh at 12 V, but repeatedly using all of that capacity is generally avoided if you want to preserve its service life.

That is why, in practice, a 100 Ah AGM battery can provide much less usable energy than a 100 Ah LiFePO4 battery.

This explains why a lithium battery with apparently the “same capacity” can provide much more real-world autonomy.

Is 100 Ah enough for a camper?

For a simple camper with LED lighting, phone charging, a water pump and an efficient fridge, 100 Ah of lithium can be enough if you recharge frequently from the alternator, solar panels or shore power.

But it may not be enough if you want to stay parked for several days, work on a laptop for many hours, use an inverter regularly or have high electrical loads.

When should you consider 200 Ah?

• You want two or more days of autonomy without recharging.
• You work from the camper.
• You use several electronic devices.
• You have a large fridge.
• You travel in winter and use the heater for many hours.
• You use an inverter frequently.
• You want to depend less on campsites and 230 V hook-ups.

Before buying 200 Ah of battery capacity, make sure you can recharge it properly. A large battery bank paired with a small charging system can take far too long to recover the energy you use.

The battery is only one part of the system

This is an important point. Replacing an AGM battery with lithium is not always as simple as removing one battery and installing another.

• Alternator.
• DC-DC charger
• 230 V mains charger.
• Solar charge controller.
• Fuses.
• Cable size.
• Isolation switches.
• Inverter.

All components must be suitable for the battery and for the currents that will flow through the system.

Do you need a DC-DC charger with lithium?

In many modern systems, a DC-DC charger is recommended to properly control charging from the alternator, especially with lithium batteries and vehicles equipped with smart alternators.

But there is no universal answer. It depends on the vehicle, alternator, battery and existing electrical system.

What if you have solar panels?

Solar panels can significantly reduce the battery capacity you need because they replace some of the energy you use during the day.

But solar production varies depending on:

• Installed solar capacity.
• Time of year.
• Location.
• Cloud cover.
• Shading.
• Panel orientation.
• Temperature.
• Charge controller efficiency.

That is why a system that works brilliantly in July can perform very differently during a trip in December.

AGM or lithium: when is it worth upgrading?

Lithium makes a lot of sense if:

• You use the camper frequently.
• You need a lot of off-grid autonomy.
• You want to reduce weight.
• You use a lot of electrical power.
• You want faster charging.
• You plan to keep the vehicle for several years.

An AGM battery can still make sense if:

• You only use the camper a few days per year.
• Your power consumption is low.
• You regularly use a 230 V hook-up.
• Your current electrical system works well.
• You want to minimise the initial cost.

Common mistakes when choosing a camper battery

• Buying based on Ah alone without calculating your consumption.
• Assuming AGM and lithium provide the same usable capacity.
• Installing lithium without checking the charging system.
• Buying a huge battery bank without enough charging capacity.
• Not checking the BMS maximum current rating.
• Ignoring permitted charging temperatures.
• Using unsuitable cables or fuses.
• Choosing purely by price without considering weight, cycle life and real-world use.

How to choose your camper battery step by step

1. Calculate your daily consumption in Wh.
2. Decide how many days of autonomy you want. (If you want to know your consumption or the days of autonomy you want to have, consult our guide on how to calculate the electrical autonomy of your campervan).
3. Calculate how much energy you can replenish each day.
4. Choose AGM, GEL or LiFePO4 according to your usage and budget.
5. Add a sensible safety margin.
6. Check that the charger, solar controller and alternator charging system are compatible.
7. Check maximum charge and discharge currents.
8. Size cables and protection devices correctly.

So, which battery would we choose for a camper?

For a camper used occasionally with modest power demands, a correctly sized AGM battery can still do the job perfectly well.

For frequent use, greater off-grid autonomy, lower weight and higher electrical loads, a properly integrated LiFePO4 battery usually offers clear advantages.

And more important than choosing between AGM, GEL or lithium is first calculating how much energy you need and how you are going to replace it..

If you are buying a used camper and want to know what else to inspect besides the battery, read our used camper buying checklist..

At Rumbante, we will continue expanding this section with guides on solar panels, charge controllers, DC-DC chargers, inverters and battery autonomy calculations.

If you want to calculate the solar part of the system, consult our guide on how many solar panels a campervan needs.

If you are going to power 230V appliances, also consult our guide on what inverter a campervan needs.