How To Charge A Leisure Battery In 5 Ways | Campervan Electrics

Campervan leisure battery charging sounds simple, but is it? Also, why do you need to charge a leisure battery?

Unfortunately, many camper conversions get it wrong and risk the health and lifespan of their leisure battery.

Don’t let this be you and your camper conversion. You want the best charging method to suit your environment, lifestyle, camper, and budget, right?

Well, you’re in the right place. We cover the different ways of charging leisure batteries to help you decide the most suitable method for you, your camper and vanlife adventures..

But first, what is a leisure battery?

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Leisure Battery Overview

To understand how a leisure battery charges, it’s beneficial knowing what one is. So, here’s a very brief overview of what a leisure battery is, how it differs from a vehicle’s starter battery and the types you can buy.

Already clued up with leisure batteries? Skip ahead to how to charge a leisure battery

Firstly, campervans have two batteries: starter and leisure. They’re similar in they store power to be used when it’s required. But, they differ in the way the stored power is used. 

Starter Battery (Vehicle battery) = High flow of power over a very short period.

Leisure Battery (Campervan battery) = Steady flow of power over a prolonged period.

What Is A Starter Battery?

A starter battery starts the engine and powers the vehicle’s electrics (headlights, radio, heater etc.). It does this by quickly providing a high flow of power (high peak current).

Starter batteries are designed to run at full capacity. However, they’re not designed to supply power when they’re not being charged. So, leaving the interior light or radio on will soon discharge the battery. 

The alternator charges the battery while the engine is running to ensure the battery remains fully charged.

Alternator: An electrical generator that is connected to the engine. It converts the mechanical energy of the engine into electrical energy. 

What Is A Leisure Battery?

Leisure batteries, also known as deep-cycle batteries, are designed to supply a steady flow of power (current) over a prolonged period.

When charged, the leisure battery will supply power to your lights, water pump, fridge, kettle, and any other appliances in your camper.

Campervan leisure battery charging is done via a battery charger that gets its power from an energy source (e.g. solar panels).

Typically, campervan leisure batteries are 12/24 volts and rated in Ah (amp hours). The Ah figure is how much power a leisure battery can store.

Types Of Campervan Leisure Batteries

Not all leisure batteries are the same, even though they may look it. Clever chemistry goes on inside them to store and provide power. The 4 leisure battery types are:

Lead-Acid (Open and Sealed)

Lead-Acid batteries come in two types; open and sealed (closed). Open lead acid batteries have open cells that require you to top them up with an electrolyte solution. Whereas sealed lead-acid batteries have closed/sealed cells that don’t require topping up.

Open lead-acid batteries can leak if they’re overfilled or not kept upright. In contrast, sealed lead-acid batteries are spill-proof and maintenance-free. 

Lead Acid batteries should only be discharged to 50% capacity. If they regularly discharge more than this, it can damage the battery. Similarly, you’ll cause damage if the battery is regularly overcharged.

Overcharged: Continued charging of a battery cell once it has reached full capacity, causing damage to the cell.

They’re the cheapest type of leisure battery, making them the most cost-effective option for people with low budgets and small electrical systems. Typically, they are best suited to short weekends and camping with electric hook-up.

AGM

AGM (absorbed glass matt) batteries use lead-acid battery technology. However, they use a fibreglass mat that absorbs the electrolyte, making them spill-proof. Also, the battery is protected from vibrations, which is perfect for campervans. 

AGM batteries should only be discharged to 50% capacity like lead acid batteries. Prolonged discharge below 50% and overcharging can lead to battery damage.  

They’re ideally suited to small or large electrical systems, preferably with battery monitoring. Typically, they work best for short trips and campsites but are suitable for off-grid use when the correct charging methods are used.

• More expensive than open/closed cell lead-acid
• Longer lifespan than open/closed cell
• High charge and discharge efficiency
• Low tolerance to overcharging and high voltages
• Can withstand heavy vibrations
• Highly suited to campervan use

GEL

GEL batteries also use lead-acid battery technology. However, the electrolyte is in gel form instead of liquid, making it impossible to spill out if the battery is damaged. They’re also maintenance-free.

GEL batteries can discharge to 80%. However, prolonged discharge of above 80%, quick charging and overcharging can lead to battery damage.

Ideally suited to all campervan electrical systems and use, especially off-grid situations when charging can be irregular. However, they’re not commonly used in the UK.

• More expensive than open/closed cell lead acid
• They can be installed in virtually any position
• Will not leak out harmful battery acid if damaged
• Slow charging rate
• Can withstand heavy vibrations
• High performance throughout its life

Lithium

Lithium batteries use advanced lithium Iron Phosphate (LiFePO4) technology to store power, making them much lighter than lead-acid technology batteries.

They can safely discharge as low as 95%, almost twice the amount of lead-acid technology. Also, they don’t suffer damage if left discharged for prolonged periods.

However, specific battery chargers are required to charge lithium batteries due to their higher charging voltage. So, upgrading to lithium from lead acid will also require a charger upgrade.

Lithium batteries are the most expensive campervan battery type on the market. Depending on the manufacturer, they can cost 2-3 times as much as lead-acid batteries. However, their lifespan is a lot longer.

• Most expensive battery type in regards to the initial cost
• Less than half the weight of equivalent lead-acid batteries
• Holds voltage better when discharging
• Can withstand high charge currents 
• Lifespan is approx 10,000 charge cycles (6x longer than AGM)
• Charge faster than GEL and AGM and over 4x faster than open/closed cell
• Cant be charged below 0˚C unless the battery is heated.
• No toxic liquid

How Does A Leisure Battery Charge?

A power source (e.g. solar power) supplies power to a battery charger. The charger converts this power into the required current and voltage to charge the battery. Inside the battery, the battery cells hold this energy for you to use later. Think of it like a dry sponge (battery) absorbing water (current).

Basic chargers supply a constant current and voltage to the battery until they’re turned off. This puts the battery at risk of over/undercharging and can reduce its life.

More advanced chargers control the output voltage and current to the battery to ensure it doesn’t over/undercharge, ensuring it stays healthy and prolongs its life.

Undercharging: The battery cell is not receiving enough charge to return it to full capacity. Prolonged undercharging will lead to premature battery failure.

This charging method is recommended and is known as ‘trickle’ or ‘3 stage’ charging.

Battery Charging Stages

3-stage leisure battery charging consists of, you guessed it, 3 stages: bulk, absorption, and float.

The charger will deliver different voltages and currents depending on the charging stage, battery type and battery charge level. Therefore, the time it takes for each stage to complete will differ in every situation.

Let’s look at each stage in more detail:

Bulk (0-80%)

The battery charger will detect the needs of the battery and deliver its maximum voltage and current. Typically, the battery will charge up to 80% at this stage.

Absorption (80-95%)

When the charge reaches 80%, a constant voltage and reduced current are supplied to the battery. Typically, the battery will be almost fully charged (95%) when this stage is complete.

Float (95-100%)

Also known as ‘trickle charging’, the charger will supply a steady current to the battery, bringing it up to 100%. The charger will then monitor the battery and keep it from self-discharging.

5 Ways To Charge A Leisure Battery In A Camper

Here’s an overview of the different campervan leisure battery charging methods.

#1 – Solar Power

Solar power converts sunlight into electrical energy through solar PV (photovoltaic) panels. This electrical energy is then stored in your campervan leisure battery.

The downside of using sunlight energy is it’s only available during the daytime when the sun is out. Also, the efficiency of sunlight energy can be hindered by obstacles like trees, buildings, clouds and even the time of year.

Even so, solar energy is free and available to harness all day, all year round. Therefore, a well-designed camper van solar system will ensure the most amount of energy is harnessed.

Solar Panels

Solar panels are typically fixed to the roof of a campervan for maximum sun exposure. However, some designs are portable, allowing you to set them up facing the sunlight for the best efficiency.

Campervan solar panels come in many different sizes, designs and power ratings, allowing you to design a solar system to suit your camper and needs.

The power rating of a solar panel is measured in Watts, which differs depending on the solar panel size, design, and manufacturer. But typically, they range from 50-300 Watts each for campervans. Therefore, a solar electrical design is crucial to ensure you get the most out of your solar system.

The harnessed sunlight energy needs to charge a leisure battery, but it can’t simply connect to the battery terminals. Instead, they need a ‘middleman’ in the form of a charge controller.

Solar Charge Controllers

A solar charge controller regulates the voltage and current from the solar panels going to the battery. This ensures the battery gets the correct power and doesn’t overcharge, undercharge or over-discharge.

Over-discharge: When the battery is subject to deep discharge, the battery capacity will be affected, making it difficult to fully charge again.

Campervan solar charge controllers come in two designs: PMW and MPPT.

PWM (Pulse Width Modulation)

PWM charge controllers act like a switch that rapidly flicks on and off. This moderates the output of the solar panels to ensure the voltage is at the right level for the battery.

• Less expensive than MPPT chargers
• Panel voltage and battery voltage need to be the same (E.g. 12v solar system – 12v battery)
• Less efficient at approximately 75%
• Provides adequate performance in campervan electrical systems with small power requirements
• Ideal for small systems where efficiency isn’t critical (E.g. short trips and weekends away)
• Cheaper build quality
• Suitable for smaller solar power systems (<300 watts)
• Ideally suited to single-panel systems. Multiple panels must be connected in parallel
• Most are only compatible with lead-acid batteries (AGM, GEL, Open, Sealed). They’re not too kind at charging Lithium batteries

MPPT (Maximum Power Point Tracking)

MPPT charge controllers use more sophisticated technology. They harvest the maximum available power from the solar panels and downrate the voltage to meet the battery requirements. The current is then boosted to compensate for the lower battery voltage and reduce energy loss.

• More expensive than PWM chargers
• Panel voltages can be higher than the battery voltage for more efficiency and system growth (E.g. 36v solar system – 12v battery)
• More efficient at approximately 95%
• Best suited to larger, more professional systems with bigger power requirements and usage
• More features (Bluetooth and charging settings)
• Better build quality
• Suitable for larger solar systems (>300 watts) and when series connecting solar panels (increases voltage)
• Ideally suited to multiple panel systems connected in series
• Compatible with all battery types, and some have custom battery settings
• Better performance in colder climates, cloudy conditions, and shade

Further Reading | The Best DC to DC Chargers With MPPT Solar

Series vs Parallel

Solar panels provide power to the battery via the charge controller by wiring them in either a series or parallel configuration (or even series-parallel like our set-up).

Each configuration results in different power outputs depending on the solar array size, usage, and requirements. However, the wattage output will remain the same in both configurations.

Series Configuration

The panels are connected like a chain – positive-negative, positive-negative.

In this example, three panels rated at 100w, 12v, 10A each are connected in series. The overall solar panel output would be 300w, 36v, 10A.

Voltage (Volts) – Increases

Current (Amps) – remains the same.

• Doesn’t like partial shade as it decreases the overall power output
• The best option for optimum battery charging
• Best suited to MPPT charge controllers
• Ideal for larger solar systems
• Cheaper – Due to the lower current, smaller cable sizes can be used.
• Ideal for 12 volt and 24 volt electrical systems
• Can get away with longer cable runs between the solar panels and charge controller due to the higher voltage (voltage drop)

Parallel Configuration

The panels are connected, with all the positives connected together and all the negatives connected together.

In this example, three panels, each rated at 100w, 12v, 10A, are connected in parallel. The overall solar panel output would be 300w, 12v, 30A.

Voltage (Volts) – Remains the same

Current (Amps) – Increases

• More efficient in partial shade conditions, as the shade only affects the shaded panel.
• Ideally suited to smaller solar systems.
• Ideal for 12 volt electrical systems
• Suitable for PWM charge controllers due to the lower voltage
• Potentially more expensive – Higher the current, the bigger the cables needed to carry the current.

Best Of Both – Series & Parallel

Connecting a solar array in series and parallel will maximise the benefits of both configurations.

In this example, six panels, each rated at 100w, 12v, 10A, are connected, so panels 1-3 are connected in series and panels 4-6 are connected in series. The wiring for the two series arrays is connected in parallel. The overall solar panel output would be;

Panels 1-3 – 300w, 36v, 10A (Series)
Panels 4-6 – 300w, 36v, 10A (Series)
Total output – 600w, 36v, 20A (Parallel)

• Still efficient in partial shading. If one panel in a series array is shaded, the other series array will be unaffected
• Suitable for 12 volt and 24 volt electrical systems
• Can ONLY be used with MPPT charge controllers
• High efficiency in low-light situations
• Best suited to larger solar systems
• Can achieve a desired voltage or current depending on your needs

#2 – Mains/Shore

Mains (also known as shore) power is the electrical power from the grid used in our homes and campsites. Mains/shore power is 230 Volts AC (alternating current) in the UK.

A leisure battery is plugged into the mains via a battery charger, where it begins its charging stages. Typically, a 3-pin household plug is used in homes, and a 16Amp blue commando socket is used at campsites.

Unlike solar, this method of charging isn’t free. However, the power is available 24/7 as it doesn’t rely on sunlight and weather conditions.

Mains Charger

Leisure battery chargers convert the 230v AC mains power into a DC power suitable for the battery type its charging (typically 12v).

Most chargers can select the battery type being charged to ensure the DC output is optimised for that battery. However, some less expensive chargers are only suitable for specific battery types.

There are two mains battery chargers for your campervan: portable or onboard. Both have their pros and cons but provide similar battery charging characteristics.

Portable Battery Chargers are the ones typically used to charge a starter battery. Put the crocodile clips onto the battery terminals and plug the charger in. They’re ideal if you occasionally charge from the mains, as they can be stored away until needed.

• Requires easy access to the leisure battery terminals
• The battery can be removed to charge, so appliance load doesn’t affects the charge
• Lower cost option
• Crocodile clip battery connections aren’t as secure, so they are more prone to a loose electrical connection that can affect charging and could cause a fire
• Can be used to charge the starter battery
• Need to be stored somewhere

On-board Battery Chargers are typically used in campervans, motorhomes, and RVs. They’re fixed and hard-wired into the campervan electrics. They’re ideal if you need to charge from the mains regularly or want the convenience of just plugging the van into the mains when required.

• Once installed, access to the battery terminals isn’t required
• It’s set up and ready for when you need it
• Fixed battery terminals provide a better and safer electrical connection
• May require ventilation to keep them cool whilst charging
• Requires a hook-up to connect it to the mains/shore power
• More features (Bluetooth and charging settings)

Mains Hook Up

A hook-up connects your leisure battery to the mains/shore power and/or alternator (we will cover alternator power next). There are many hook-up kits available, but generally, mains hook up consists of a:

• Mains hook up lead to connect the camper to the mains/shore power point.
• Campervan mounted hook up lead socket.
• 230v AC consumer unit with RCD protection and double pole circuit breakers.

#3 – Alternator/Driving

An alternator is an electrical generator that is connected to the engine. It converts the mechanical energy of the engine into electrical energy.

The alternator charges the vehicle starter battery and provides power to the vehicle’s electrics while the engine runs. So, why not use the alternator to charge a leisure battery too.

It’s a simple yet complicated method. It’s simple because the leisure battery only needs to connect to the starter battery via a relay or charger. It’s complicated because you need electrical design and knowledge to ensure the alternator doesn’t burn out and the leisure battery is charged efficiently.

There are two ways to charge a leisure battery from the alternator, via a voltage sensing relay (VSR) or battery to battery charger (B2B).

Further Reading | The 6 Best Campervan Battery To Battery Chargers 2023

VSR (Voltage Sensing Relay)

A VSR (Voltage Sensing Relay) is a switch that will supply power to the leisure battery when the alternator reaches charging voltage (i.e. when the engine is running).

When the engine is off, or the charge voltage drops below a certain level, the VCR disconnects the starter and leisure batteries. Thereby ensuring the starter battery isn’t drained when using your campervan electrics and the leisure battery isn’t used to start the engine.

• Simple to wire and install
• Simple technology
• Cheapest option
• No modifications to the vehicle electronics
• Doesn’t go through charging stages.
• Can’t be used with smart/intelligent alternators found on Euro 5 & 6 engines (2015 onwards)
• Only charge when the alternator produces a charging voltage
• Doesn’t drain the starter battery
• Not recommended for Lithium batteries, only lead-acid
• Up to 80% battery charge rate

DC To DC Charger (Battery to Battery)

A B2B charger, also called a DC-DC charger/converter, works with the alternator to charge a leisure battery. Like the VSR, it acts a switch to connect and disconnect the leisure battery to the starter battery.

However, unlike a VSR, B2B chargers convert the power from the alternator to suit the battery charging requirements. This ensures the battery is charged efficiently and will prolong its life.

• More expensive than VSR
• Ignition switch wiring is required
• Charging all the time the engine is running.
• Goes through charge stages like a mains charger.
• Doesn’t drain the starter battery
• Faster charge rate
• Can be used on any vehicle
• Some models and vehicles require ignition switch wiring
• Charges all battery types.
• 100% battery charge rate

Further Reading | Our Honest Review Of The Renogy 40A DC to DC Battery Charger

#4 – Wind

Wind turbines convert wind energy into electrical energy. The wind turns the propeller blades that then spins a generator, producing electricity.

Wind-generated power is less common in campervans because it’s not a ‘fixed’ charging method, like solar. For example, you can’t drive down the road with a wind turbine on the roof. So, it will need to be set up wherever you go.

• With enough wind, they can produce power all day.
• Require setting up and storing away.
• Expensive in relation to power output and installation cost
• Less efficient and productive at charging than other methods.
• Ideal for off-grid van living.
• The right amount of wind speed is required. Too low, they won’t work. Too fast, and they could break.
• Can be noisy (although we’ve slept in a wind farm and not been disturbed by the noise).
• Could be a lightning risk.
• Ideal for winter charging when solar energy is low.
• Good method of charging small appliances
• Ideal as a secondary charging method.
• Requires a battery charge converter.

#5 – Generator

A campervan generator is a small, portable engine that turns an electromagnet, producing electricity. Basically, as long as you have fuel, you have power – great!

A generator is an alternative charging method when you can’t use mains/shore hook-up. So, they’re ideal for wild and off-grid camping. Additionally, their power output isn’t affected by weather conditions.

Unfortunately, they’re noisy, so they can’t be used everywhere. Most places have restrictions on where they can be used. However, some models have an eco-mode, which runs surprisingly quietly.

Leisure Battery Charge Monitoring

A leisure battery monitor will help you get the most out of your battery by monitoring the charge and capacity levels, known as SOC (state of charge).

There are many ways to monitor a campervan leisure battery, from manually measuring the battery terminals to a clever kit called a shunt.

Either way, introducing battery monitoring to your installation will ensure you always know how much power is available. Therefore, you will know when the battery needs charging, which will help you take better care of it.

It’s important to note that Lead-Acid, AGM, GEL and Lithium batteries have different charge rates regarding their voltages and DOD (depth of discharge) levels.

Here’s a chart to explain the differences:

Manual Measuring

This is the most basic and cheapest level of battery monitoring. Still, it’s a good way to understand the battery charge levels. However, it does require some electrical knowledge to carry out.

Using a voltmeter, measure the voltage between the positive and negative battery terminals with all loads and chargers turned off (known as ‘no-load’). This is to ensure you get an accurate reading of the battery. This voltage reading will determine the approximate SOC of the battery and give you an idea of how much power it has left.

Manual measuring is less practical because you need easy access to the battery terminals, so daily monitoring can be a chore. Also, you will need to measure the battery readings throughout the day to get an accurate SOC.

• Ideal for tight budgets
• Best suited to low-use and short trips
• Requires electrical knowledge
• No installation is required
• Requires access to the battery terminals
• Test must be carried out with no loads or charger power
• Approximate level of monitoring
• Unhealthy for the battery

Voltage And Current Monitors

These devices are wired into the electrical system between the battery and the load. They will monitor the battery’s real-time voltage and load current via an analogue/digital display.

A voltage meter will tell you the voltage of the battery. It’s a more practical way of monitoring the battery SOC. However, you still need to know what the voltage level relates to (see charts above).

A current meter will only tell you the current being used at that moment. So, it requires regular monitoring and some maths to work out the available Ah’s (Amp hours) remaining in the battery.

For example: Your lights are on, and the current meter is showing 5Amps. If the lights are on for an hour, the battery will use 5Ah of power. However, if the lights are on for half an hour, the battery will use 2.5Ah of power.

So, from this example, you can see it’s not a practical way of monitoring the battery.

• Ideal for smaller electrical installations
• Cheap
• Not very accurate: voltage can fluctuate due to temperature and other environmental conditions.
• SOC requires calculating
• Correct installation is crucial for accurate readings.
• Accessible battery monitoring
• Requires ‘no-load’ voltage for an accurate reading

Percentage Monitors

A percentage monitor is essentially a voltmeter, as described above, but instead of showing a voltage figure, they indicate the charge level in the battery by a percentage (although some show both the percentage and voltage).

These monitors do the hard work of calculating the SOC, so you don’t have to refer to the charts. The charge level is shown by different coloured LED’s, so the SOC is easy to understand.

• Ideal for smaller electrical installations
• Cheap
• Correct installation crucial for an accurate reading
• Easy to understand and accessible monitoring
• Estimated SOC percentage
• Requires ‘no load’ voltage for an accurate reading

Shunt Monitors

A shunt is a resistor that monitors the real-time voltage and current flow into and out of the battery. Resulting in a very accurate SOC reading once the shunt has been set up with the leisure battery parameters.

They provide a wide array of information, including SOC %, voltage, current draw, charge current and even Ah remaining in the battery. This information is shown as a figure, resulting in very accurate monitoring.

Some models have additional features like audible alarms to warn you and relays that trigger under certain battery conditions (E.g. switching on a charger when the battery is low)

• Most expensive
• Must be configured with battery to give accurate readings.
• Unaffected by battery load and being charged
• Helps optimise battery performance
• Accurate battery SOC
• Straightforward installation
• Does the calculations for you and displays the results

Recap

So, now you know the 5 ways to charge a leisure battery and the importance of efficient leisure battery charging.

Whether your a weekend warrior or full-time vanlifer, you can now decide which method suits you, your camper and your adventures.

Further Reading | See All Campervan Electrics Posts