All You Need to Know about Charging a Motorhome Battery

Your motorhome electrical system is your lifeline to modern civilisation, comfort and convenience. When connected to mains power, it will distribute 240 volts (V) to the three-pin sockets located throughout your motorhome cabin.

But what about when you’re not connected to mains and you have to rely on battery power to camp in comfort?

In this article, we talk about motorhome batteries, where their power comes from, and how to safely recharge them from different sources.

The motorhome house battery

Your motorhome will have a house battery — otherwise known as a leisure battery. It stores a 12V reserve of power — as a single deep-cycle battery or sometimes two connected in tandem.

When you’re parked up without access to mains, this is the power that will supply your:

• Lighting

• Device charging at any USB ports

• Entertainment systems.
  
  

In some smaller motorhomes or campervans, the 12V house battery power storage is often used to run a fridge that can’t be switched over to gas while freedom camping.

Where does your house battery’s power come from? 

Your motorhome or campervan’s house battery is replenished with electrons supplied by the two onboard chargers. These chargers are usually located near the fusebox and main electrical on-off master switch of your recreational vehicle.

The storage battery that the chargers serve is often located directly below the front passenger seat of your motorhome. It’s almost never found under the bonnet in the engine bay — although there are some exceptions.

Volkswagen’s Grand California campervan models have the house battery located in the engine bay. However, the battery that starts the engine and powers mechanical ancillaries is mounted beneath the passenger seat.

The reasons for two motorhome battery chargers

When travelling around in your motorhome, the house battery will have two ways of charging.

Direct current to direct current

One is the direct current (DC) to DC charger which takes direct current from the engine alternator when driving and uses it to top up the power in your house battery.

This charger will also trickle-charge your battery from any solar panel fitted to the roof of your motorhome — with the process monitored by a solar power controller.

Alternating current to direct current

Alternating current (AC) to DC is the other charger that converts any alternating current supply — like from a campground power site or separate generator — to 12V of direct current and stores it in your house battery.

Take a look at our other safety blogs — using LPG safely and seatbelt safety.

Guidelines for recharging your house battery

It’s best to think of storing power with a similar mindset to your approach to water storage. Your water tank acts as a reservoir — and so should your battery.

The major difference is that you must replenish the power in your battery when it’s:

• Still half full — in the case of lead acid and AGM batteries

• Around one fifth full — when it comes to lithium-ion batteries.
  
  

Discharging your battery lower than these levels can result in irreparable damage. Be sure to regularly check your campervan’s battery monitor to help maintain your house battery’s health.

Power storage levels will be more resilient if you have solar panels fitted — but their performance is drastically reduced by cloud cover.

Ritual battery monitoring is a good habit to get into even when there’s solar panel back-up installed.

How to carefully charge your battery from a 240V source

Common 240V power sources for recharging 12V house batteries are:

• The national grid mains supply — located in a nearby building

• A stand-alone generator — that chugs away quietly next to your parked motorhome

• A 15A connection socket — found at the top of a post on a power site at a campground or holiday resort.
  
  

Amps measure the flow of current from a plug to your motorhome, and the voltage of that current will be a constant 240 volts. This voltage is high enough to be fatal should a fault occur — so we’ve outlined the safest step-by-step methods for recharging from each source.

National grid mains supply

This option is powered via a 10A outlet socket from your nearest building. Here’s how to utilise this power.

1. Identify the ideal position to park your motorhome in relation to the building while taking into account:

1. Shelter from the weather

2. The length of the power cable

3. Whether your cable adapter is weatherproof or must remain indoors.

   Ideally, the space between your motorhome and the building is rarely frequented by children or pets.

2. Position your motorhome so that its power cable input socket is on the sheltered side of any prevailing wind, if possible.

3. Deploy the power lead so that it’s completely uncoiled with no contact between loops of the cable.

4. Plug your cable into the input socket on the side of your motorhome.

5. Carefully place the other end of your cable inside the building — through either a partially open window or a garage door.

6. Attach the adapter to the other end of the cable.

   Position the cable on some form of support near the domestic supply socket — so that it won’t hang down and dislodge the connection when connected to the mains.

7. Plug the adapter into the supply output socket and switch the latter on.

8. Check the battery monitor inside your motorhome to make sure your house battery is being charged. If it isn’t:

1. 1. Turn off the domestic supply

   2. Flip over the tab on the adapter’s circuit breaker — as it often gets flipped while in transit

   3. Switch the source power socket back on

   4. Recheck your battery monitor

   5. If there is still no power flowing to your motorhome, check the fuse box inside the building — to see if the circuit breaker for that socket has been triggered.

Stand-alone generator

Sometimes a building with 240V power simply isn’t available. A portable generator allows you to go to plan B when your house battery needs recharging.

Preferably, choose a generator that:

• Runs on less poisonous petrol than diesel

• Has efficient noise and emission suppression

• Already comes with the same 15A output socket you find serving power sites in most camping grounds.
  
  

Mains hookup remains the quickest way to recharge your house battery but if a generator is your only resort, here’s how to go about it.

1. Place your generator at least a metre away, and:
   
   

   1. Downwind from any open motorhome doors or windows

   2. On a flat level site

   3. Sheltered from the elements.
      
      

2. Start the generator and allow the motor to warm up before plugging your motorhome’s power cable into the 15A outlet socket.
   
   

   If your generator only has a 10A outlet socket, you’ll need to have the cable adapter that’s used when charging from a house plug handy.

3. When your generator motor is at operating temperature:

   
   

   1. Plug the power cable into the input socket of your motorhome

   2. Then attach the other end to the outlet socket of your generator — using the adapter if the generator has a 10A outlet socket.

4. Turn off the eco mode on your generator as you’ll want it to operate at full capacity.

If your house battery was fairly depleted before connecting to a generator, just be aware that it can take 8-10 hours to fully charge.

Campground 15A connection socket

Pulling into a camping ground every few nights will give you the opportunity to take advantage of their facilities — including the 15A power outlet sockets that serve each site.

Here’s the safest way to plug in.

1. First, inspect your site’s power supply — as the outlet socket should be in a clean condition accompanied by a circuit breaker in an equivalent serviceable state.

   
   

   If it’s covered in cobwebs and mounted on a corroded plate, ask if you can use another site with a power supply that’s better maintained.

2. Deploy your power cable so that it reaches both the supply outlet and your motorhome — without any loops coming into contact with each other.

3. Plug the motorhome end in first and repeat the process at your site’s supply outlet.

4. Check the battery monitor inside your motorhome to ensure that the house battery is being charged.

If it’s not, then it’s likely that the circuit breaker near the site’s supply socket was already triggered when you connected the power cable. Disarming the circuit breaker should enable power to flow from the site to your house battery.

Using the DC to DC charger

Firing up your diesel engine will immediately activate your motor’s ancillary alternator. This will feed 14V of power to the DC to DC charger — with the direct current flowing at 140A.

Your house battery will steadily recharge with the engine at idle speed but charging at low revs can accelerate the wear of the diesel engine’s valve train and cylinder bores.

Some RVs, like the Grand California from VW, come with fast-idle buttons to allow safe recharging of the house battery without the need to move.

A far better way to recharge your house battery using the engine alternator is to simply take your motorhome for a drive. An hour-long trip will fully recharge a depleted house battery.

For more information on motorhome power, check out our guide to 12V batteries.