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How to Charge A Leisure Battery & Maintain A Healthy Battery In Your Camper

Do you want to know how to charge a leisure battery and keep your camper’s batteries in tip-top condition? There are 4 ways for you to try – each with its advantages and disadvantages. Keep reading to learn everything there is to know about charging your leisure battery!


Charging leisure batteries in motorhomes, RVs, campervans, and caravans is essential.

The batteries will flatten without an effective means of replacing the energy used. 

Not only is it essential to recharge them so you can continue to use them, but if left too deeply discharged for too long, their lifespan will shorten.

This post introduces the 4 ways of charging a leisure battery bank.

How To Charge A Leisure Battery | 4 Methods

There are a few different ways to charge a leisure battery. Campervans, motorhomes, and RVs often use more than one method, providing recharging options no matter where they’re camped.

If you maintain the batteries’ charge, you can help prolong their life and provide the power you need to keep gadgets and appliances running.

Regardless of the battery type, there are 4 ways of charging a leisure battery in a camper:

  • Charging batteries while driving
  • Campervan solar panel system
  • Hook up battery charging
  • Using a generator

A good all-round campervan electrical system includes at least 2 or 3 of these charging methods. A versatile setup is ideal for those who travel, use campgrounds occasionally and enjoy camping off-grid.

Before we get into the detail of how to charge a leisure battery, let’s consider how campervan batteries work and get recharged.

Overview Of Campervan Batteries

The leisure batteries we install in our campers aren’t the same as the starter battery under the hood.

Starter batteries are designed to provide a big burst of energy fast and use as much as 20% of their total capacity per start.

Once the engine starts up, the alternator recharges the starter battery, so it’s primed for the next time you start it up.

Unlike starter batteries, a deep cycle battery (or leisure battery) is designed to release energy in a steady flow over a longer period. 

They can discharge a lot of their energy in a longer, deeper energy drain, which would kill a starter battery quickly.

This post focuses on how to charge these leisure batteries. They’re often called house batteries, 12v batteries, or deep cycle batteries, just to keep us on our toes!

There are 4 types of leisure batteries on the market:

  • Flooded lead-acid (FLA)
  • Gel batteries
  • Absorbed glass mat (AGM) batteries
  • Lithium-ion batteries

Each of the 4 battery types uses slightly different chemistry, so the way they work and perform is different. 
That’s all you need to know for this post. Check out our article on campervan batteries if you want to learn more about battery types and how to connect them.

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How Does A Battery Get Charged?

Lithium batteries are similar to your laptop battery - charged or not, on or off

A battery is an electrical store of DC power measured in amp hours. 

Some of that electrical store is used up by your camper’s 12v appliances. To replace the used energy, we need to recharge it.

Batteries draw current from an available voltage supply, replenishing the energy.

Think of the battery like a sponge.

Place a slightly damp sponge on water, and it quickly soaks up a lot of water.

A deeply discharged battery behaves this way too. Provide it with a voltage supply, and it draws as many amps as it can.

As a sponge becomes more saturated, the rate at which it continues to absorb water slows. 

A battery behaves this way too. The charging rate slows the more charged it becomes.

Once a sponge is completely saturated, it doesn’t take on more water. Left in the water, though, it never dries out either.

It’s the same for the battery. Once it’s fully charged, even with a voltage supply, it only takes on enough current to prevent it from discharging.

Take a sponge out of the water; over time, it begins to dry out, even without wringing it out. 

Again, a battery behaves this way too. Without a constant voltage supply and even without any load, a battery will slowly release its charge over time.

If the sponge is allowed to dry completely, it becomes dry and hard. A bone-dry sponge floats on water and can take a while to soak up water. 

A flat battery behaves similarly. Unfortunately, depending on the type of battery, how long it’s been flat, and whether you have luck on your side, a flat battery may never recover.

These different stages of charging a battery are determined by its charging profile.

3 Stage Battery Charging

While all batteries have stages they go through to charge, they are slightly different between lead-acid and lithium.

The principle, though, is the same and the detailed charging profile of each battery indicates the more significant differences.

Bulk Charge | The battery is low and will take as much current available (up to its maximum charge rate). This stage usually brings the battery up to about 80% charge.

Absorption Stage | The battery is so full at the end of the bulk charge phase that its resistance is relatively high. Therefore, to absorb more current, the supply voltage needs to increase. 

It’s a bit like inflating a tyre. The more inflated it becomes, the more force is needed to pass air into it.

As the supply voltage increases, the current falls. This means that while the battery charge increases, it does so at a slower rate than in the bulk charge stage.

The voltage increases with the battery’s charge, the current falls, and the charging speed declines. 

The absorption phase continues until the battery is fully charged.

Float Charge | The stage basically maintains the battery in a fully charged state. Just as keeping a sponge in water prevents it from drying out, providing a battery with a float charge prevents it from discharging.

3 stage battery charging diagram

Battery Charging Profiles

A battery charging profile is basically an algorithm for optimum charging of the battery.

As you can see from the graph above, there’s a smooth transition between charging stages.

Different battery types have different charging profiles. 

We want to provide the battery with a voltage that closely matches its charging profile for efficient charging.

lead acid adn lithium battery charging profiles

The basic principles of battery charging are similar. Even so, there are many differences between charging lead-acid and lithium-ion batteries.

Lithium-ion batteries hold their charged voltage at about 13v until they’re almost wholly depleted, i.e., about 1%. 

Their charging profile is quite different from that of the lead-acid alternatives.

You can use them soon as you put a charge on them, even when they’re extremely low, just like a laptop battery.

Lithiums can take high currents but don’t like high voltages, so their charging profile is significantly flatter and faster.

This often means electrical components aren’t always compatible with all battery types. 

As such, always check that your components work with your chosen battery.

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1. How To Charge A Leisure Battery While Driving

Every engine has an alternator.

It’s basically an electrical generator with a diode pack to convert its AC output to DC. 

When a vehicle’s engine is first cranked, the alternator doesn’t generate electricity until it reaches about 2000 rpm. 

At 2000 rpm, the alternator generates a high enough voltage to strike the diode pack and start outputting DC power.

It then kicks out a constant voltage (usually between 13.8v and 14.4v) until the engine is switched off, even when the revs drop to less than 2000 rpm.

A vehicle uses the generated electricity to recharge its starter battery. It also powers onboard electrics like headlights, radio, and windscreen wipers.

But we can tap into this to recharge the leisure batteries too.

There are 2 methods of using the alternator’s output to charge our onboard leisure batteries:

  • Traditional split charging, and
  • Battery to battery charger.

Charging A Campervan Battery With A Split Charge Relay

A split charge relay is a device connecting the starter battery and the camper’s house batteries together. 

There are different types of split charge methods. Still, they’re all similar in that they direct voltage generated by the alternator to the leisure batteries. 

Cheap, simple solutions include an isolator switch, split charge relay, and voltage-sensitive relay.

Read more: How To Charger A Campervan Battery With A Split Charge Relay

Battery To Battery Charging

Some engines, especially on modern vehicles, have smart alternators. When they sense the starter battery is full, they reduce their voltage. 

But that’s the opposite of what we need to charge the camper’s leisure batteries. So a B2B charger has to, in effect, “trick” the alternator.

A B2B charger senses the increased voltage when the engine is running. It switches itself on, taking power directly from the starter battery. 

The smart alternator “thinks” the battery is never full, so it continues to supply it with a voltage. The B2B charger directs that to the leisure batteries.

A battery to battery charger controls the voltage sent to the leisure batteries based on their optimum charging profile. 

This is a more expensive solution but more intelligent, too. So it is possible to fully charge your batteries while driving. That isn’t possible with a split charge relay.

Read more: How To Charger A Campervan Battery With A Battery To Battery Charger

Split Charge Relay vs. B2B Charger

So should you choose a split charging system or a B2B charger?

There are some circumstances where a traditional split charging system like an isolator switch or smart relay might be appropriate.

But there are some situations where they won’t work or fall short.

The type of batteries, the entire charging setup, and your intended van lifestyle should help inform your decision.

Here are a few points to consider when deciding which (if any) is best for you.

Working the alternator

Motorhome or campervan in front of snow covered Scottish Highlands

Both B2B chargers and split charge relays make the vehicle’s alternator work harder than it was designed to. In effect, this shortens the life of a vehicle’s alternator, and replacing them isn’t cheap!

Always check the vehicle manufacturer’s recommendations on the maximum size.

Avoid split charging altogether if you can rely on recharging the batteries without driving. Or at least fit a component you can manually switch off.

Split charge relays don’t fully charge leisure batteries

Remember we talked about the bulk stage of battery charging? Isolator switches and other split charging devices only provide a bulk charge to the batteries.

You can never fully recharge the battery bank by driving alone. 

If you rely on charging leisure batteries while driving, a B2B charger is probably essential. It’s the only way the batteries can be fully recharged. Without this, the battery life is negatively affected.

Battery to battery chargers can fully charge a leisure battery

B2B chargers take the voltage from the alternator and regulate it to closely match the charging profile of the battery bank. 

They’re generally programmable components, so they are configurable for your specific battery. That means you can fully charge your leisure batteries while driving if you drive for long enough.

Lithium-ion batteries

Lithium-ion batteries don’t take kindly to overcharging. As a result, their charge profile has a much smaller voltage tolerance than lead-acid alternatives.

As such, only use the battery to battery charger recommended by the battery manufacturer. 

Lithium batteries are too expensive to take risks with. 

Smart alternators

Many modern vehicles are now fitted with “smart” alternators to improve the fuel efficiency of the vehicle. 

Because their alternators don’t constantly generate electricity, they are more environmentally friendly. 

Most of what we’ve read about smart alternators suggests you can only charge the leisure batteries with a B2B charger. A split charge relay won’t do the job. 

We’re yet to be convinced of the logic behind this.

We accept the B2B is far better at charging the batteries than a smart relay. 

However, smart relays work by joining the starter and house batteries. So why would a smart alternator not continue to run? 

Our van doesn’t have a smart alternator, so it’s not an issue for us. But, we think a smart relay (VSR) will work fine, although it’s unable to fully recharge the house batteries.

If you can shed light on this, please leave us an explanation in the comments below. It’s driving us crazy!

Both B2B chargers and split chargers make the alternator work harder than it was designed to. In effect this shortens the life of a vehicle’s alternator and replacing them isn’t cheap!

Always check the vehicle manufacturer’s recommendations on the maximum size.

If you can rely on fully recharging the leisure batteries without driving, avoid split charging altogether or at least fit a component you can manually switch off.

Split charge relays don’t fully charge leisure batteries

Remember we talked about the bulk stage of battery charging? Isolator switches and other split charging devices only provide a bulk charge to the batteries.

As such, you can never fully recharge the battery bank by driving alone. 

If you rely heavily on charging leisure batteries while driving, a B2B charger is probably essential because it’s the only way the batteries can be fully recharged. Without this, the battery life is negatively affected.

Battery to battery chargers

B2B chargers take the voltage from the alternator and regulate it to closely match the charging profile of the battery bank. 

They’re generally programmable components so configurable for your specific battery.

Lithium-ion batteries

Lithium-ion batteries don’t take kindly to be being overcharged and their charge profile has a much smaller voltage tolerance then the lead acid alternatives.

As such, only use the battery to battery charger recommended by the battery manufacturer. 

Lithium batteries are too expensive to take risks with. 

Smart alternators

Many modern vehicles are now fitted with “smart” alternators to improve the fuel efficiency of the vehicle. 

Because they don’t need to generate so much electricity from the alternator, these vehicles are more environmentally friendly. 

Most of what we’ve read about smart alternators suggest you can only charge the leisure batteries with a B2B charger (rather than a split charge relay). 

We’re yet to be convinced on the logic behind this.

We accept the B2B is far better at charging the batteries than a smart relay. 

However, smart relays work by joining the starter battery to the house batteries too. So why would a smart alternator not continue to run? 

Our van doesn’t have a smart alternator so it’s not an issue for us but we think a smart relay (VSR) will work fine, albeit with the limitations of being unable to fully recharge the house batteries.

If you can shed light on this, please leave us an explanation in the comments below. It’s driving us crazy!

2. Using A Campervan Solar Panel System To Charge The Battery

Wiring up RV solar panels

A well-sized campervan solar panel system is the ultimate way to keep leisure batteries charged for off-grid living.

Installing solar panels on a camper is relatively simple. Even so, it’s important to size the system to meet your needs and choose the right component parts.

We have a series of articles on campervan solar panel systems to help you through the process.

Here are a few of the critical points by way of a summary:

  • Camper solar panels harvest the sun’s energy, converting it to DC power
  • Wiring panels in series or parallel alters the amount of power they can generate
  • A solar charge controller regulates the voltage from the panels for the batteries to draw current from
  • PWM charge controllers are low cost but inefficient, especially for larger solar panel setups
  • An MPPT charge controller is highly efficient at eeking out as much voltage from the panels as it can

It’s important to size a solar system to work with the battery bank. Undersize the panels, and you may not fully recharge the batteries.

Oversize it, and it’s a waste of money and roof space.

Read more: Use our solar calculator to size your system.

3. Hook Up Battery Charging

RV hookup to shore power

For those who spend any time on campgrounds with a main power supply, an AC hook-up (240v or 110v) is a perfect way of recharging leisure batteries.

You can plug the camper into a mains supply with the proper setup.

AC power is delivered to a breaker box, just like in a house.

This allows you to use AC appliances on a mains circuit – ideal for running air conditioning units and microwaves.

A battery charger (or power converter) takes the AC power, converts it to DC, and charges the leisure batteries too.

The best power converters offer multi-stage charging. These will closely match the charging profile of your battery bank so you can be confident it can be fully charged.

Most custom-built RVs and motorhomes include in-built battery chargers as standard.

When buying a campervan, new or pre-loved, it’s worth checking if the battery charger is a multi-stage or single-stage device.

For more details, check our complete guide to RV converters & battery chargers.

If you’re building your own conversion, you’ll need to install a campervan hook-up facility and a battery charger (often called a power converter).

4. Charging Leisure Batteries With A Generator

generator in a forest, clean energy is better for our environment and health

RV generators work on the same principle as using a mains supply. The onboard facilities remain the same for portable generators. They simply take the place of the AC pedestal.

So, instead of hooking up to the mains supply, you plug into the generator.

It is crucial that you don’t connect your generator and mains hook-up at the same time. It’d make for a bad day! RVs with built-in generators have a transfer switch to ensure that can’t happen.

How We Charge Our Leisure Batteries

Mercedes Sprinter 4x4 camper van driving in Torres del Paine

We’ve lived in our Sprinter van conversion since 2018 and live off-grid as much as possible.

We rely heavily on our campervan solar panels for charging leisure batteries.

320 watts of solar, wired in series with an MPPT controller, keeps our 230ah gel batteries nicely charged.

For alternator charging, we use a manual switch. We could never fully charge our batteries from this, but because of the solar, we don’t need to. 

And anyway, we don’t drive far enough, often enough, even if we had a battery to battery charger.

We also have a hook-up capability with a 30amp battery charger we use on campgrounds.

We’ve just survived living in the van in winter (a chilly Patagonian winter) without much driving and no hook-up, so we’re pleased with our setup.

You can read more about our camper’s electrical design here.

Checking Leisure Battery Charge Levels

A simple voltage meter can indicate the battery charge level. It measures the voltage at the battery terminals.

This is all we use in our DIY van conversion to keep an eye on the charge levels.

But many far more sophisticated battery monitoring systems and power management systems are available on the market too.

The voltage of a lead acid batteries compared to lithium for their charging states

Many of these even allow you to monitor battery health remotely!

Regardless of what type of lead-acid battery you opt for, the charge level of lead-acid batteries is indicated by their voltage.

For the best long-term health of lead-acid batteries, avoid discharging them over 50%.

Because lithium batteries hold their charging voltage, a battery management system is essential.

Lithium batteries cope well with being fully discharged, though.

For the best long term health of lead acid batteries, avoid discharging them over 50%.

Because lithium batteries hold their charging voltage, a battery management system is essential to monitor how charged they are.

Lithium batteries cope well with being fully discharged though.

In Conclusion

​​And there you have it, four ways to charge your leisure battery. 

  • Solar panels are great if you’re off the grid, but they can be a bit pricey to set up. 
  • If you’re often plugged into the mains, that’s the easiest way to go. 
  • Generators are noisy and smelly, but they’ll get the job done in a pinch. 
  • And finally, if you’re on the move, you can charge your battery while you drive. 

Let us know in the comments below what combination of these methods you use to charge your camper’s house batteries.

Andy Williams

Monday 3rd of October 2022

Hi Use a 12v battery to heat up a 12v food warner in the back of my golf buggy, once i have finished golf i plug it in to a 240v charger, but for some reason its not holding its charge! do i need to hook it up to an engine and fully charge it that way?

Roy

Sunday 21st of August 2022

How long can you leave mains input in for charging leisure battery for.

Angela and Graham

Thursday 1st of September 2022

Hi Roy, You can leave it plugged in for as long as you want. Once the battery is full, it won't take any further charger. Hope this helps.

Richard Campbell

Saturday 7th of August 2021

I have owned 2 nissan nv200 self conversions each of which had/have a 'smart' alternater. I fitted a voltage sensing relay (cyrix) to both. No problems with either vehicle (10 years combined use) and approx a tenth of the price of a btob unit. I agree that the system doesn't charge the leisure battery fully but feel that it's a small price to pay for the financial saving! - Richard

David

Thursday 11th of February 2021

Hello,

Can you tell me how you switch the charging of the batteries from solar to mains? Is this done automatically, or do you use a switch?

Many thanks.

Angela and Graham

Thursday 11th of February 2021

Hi David, Yeah it's automatic. They both provide a voltage to the battery terminal simultaneously. Same if you're driving and have a B2B or split charge relay. The combined voltage from the alternator and the solar panels is available to the battery bank to draw on. Angela