How to Charge RV Battery With a Generator?

Last Updated on January 2, 2025

An RV battery is vital to the comfort of your next camping trip or weekend away. All your appliances onboard your motorhome rely on it to power them, so it is important to make sure it is always charged correctly.

We’re talking lights, fridge, fan etc, things you don’t want to go without. Therefore, you want to make sure you know how to charge it in the right way, to extend its life and maintain its power and make sure you get the best performance possible.

Can you charge the battery with a generator? Yes, using a generator is a common way to charge an RV battery. This can be a generator that is inbuilt into your motorhome or even a portable generator. In some cases you could also use wind or solar power if you have it installed. So let’s dive into how to efficiently and safely charge your battery with a generator.

What is an RV battery?

First things first, what actually is an RV battery?

Recreational vehicles usually use deep-cycle batteries. These are lead acid batteries, similar to car or boat batteries. The great thing about these batteries is that they produce steady current over an extended period of time, perfect for powering your appliances.

There are a variety of different types of deep-cycle battery, many of which need special maintenance to keep them working. An alternative to deep-cycle batteries for your RV are lithium batteries. These are a smaller, lighter, upgraded battery option but they are also much more expensive so not in everyone’s reach.

And what about the battery system? Your RV generator battery is normally made up of two different systems. One is a more powerful 120 volt AC system. This works to power the bigger appliances and built-in systems like air conditioning and the fridge. As this needs a lot of power to run, it only charges when the RV is running, the generator is on, or it is plugged into shore power at your camping spot.

The second, smaller, system is typically a 12 volt DC system. This powers the smaller electricals such as interior lights or fans. This 12-volt battery (or sometimes 6 volt) is the one you will be charging with your generator so that you can use it at any time.

How to charge an RV battery with a generator?

Ok, so now we understand what we are dealing with, let’s check out how to actually charge an RV battery with a generator. There are two different methods for this, using your RV’s inbuilt generator or a portable generator.

The inbuilt generator method

The inbuilt generator, or battery charger, in your RV is designed as the main source of power to run your 12 volt power system. However it is not specifically designed to charge your batteries.

When you plug your RV into a power source, it does however both power your appliances and charge your batteries at the same time (using a converter that converts 120 volts AC to 12 volts DC). Charging this way can take a lot longer than using a portable generator, especially if you are running appliances at the same time.

Step 1: Check your plug compatibility

First it is best to make sure that your shore power plug on your RV is compatible and ready to plug in to your power source. Ideally you will find a 15A plug which is shaped like a normal household plug which you can plug straight in. You may have a 30A plug, on the otherhand, which may need an adaptor to plug in. 15A and 30A plugs are compatible with 120 AC power, while for a 50A plug you may need a more powerful generator.

Step 2: Unplug everything unnecessary

From the A/C to lights or fans, for maximum and most efficient charging unplug all your electricals that are plugged into the power system. Running appliances doesn’t stop it charging the battery but it can slow it down a great deal, so don’t worry if there is something vital you need to leave running like your fridge! Nothing can ruin a trip like spoiled food!

Step 3: Prepare the generator

Before you begin you should top up your generator with fuel to make sure that it will fully charge your batteries. It can also be a good idea to run the generator for a few minutes first before you plug in the RV.

The portable generator method

Using a portable generator can be a much quicker and more efficient method than using the built in generator from your RV. Ideally, you will need to purchase a smart charger, or a three-stage charger, to be able to effectively charge your battery. Make sure to follow the steps to charge efficiently and safely while helping to elongate battery life.

Step 1: Check your generator

Without a full generator, how can you expect maximum charge? Generators are usually powered by gasoline, diesel or propane. Before starting make sure you chack the fuel levels and top up your generator to the ‘full’ line. This will help you charge your battery fully, with no nasty power outages later.

Step 2: Prepare your battery

Before you start you should also check and prepare your battery to be charged.

The first port of call is checking it for damage, leaks, corrosion or deformation to avoid causing further damage when charging as well as keeping yourself safe. Remove the battery cables before starting this process, removing the negative one first and the positive one second.

It is then important to check for dirt and buildup on the battery terminals and to clean this off. How to clean this safely? Create a paste from baking soda and water and scrub at the terminals with a small brush, an old toothbrush works perfectly.

Make sure they have fully dried before moving on. Why is it important to keep your battery maintained and clean? Dirt and damage can ruin the life of your battery and lead to it losing charge quicker and quicker.

Next you need to check the battery’s electrolyte levels. Make sure to top it up with distilled water if the fluid levels look low. Then reattach your cables to the battery, this time attaching the positive one first and the negative second. Now your battery should be ready to go.

Step 3: Unplug everything unnecessary

In this method it is wise to unplug any electricals that you are not using so as not to drain the power. Alternatively if your RV has a disconnect switch, flip this to stop power being sent to any appliances.

Step 4: Plug in

Now it is time to plug in your battery charger and your battery. Three-stage battery chargers are great as they reduce your charging time and efficiency by far. They automatically adjust their power to avoid over charging your batteries and damaging them. You can plug the charger straight into the generator and wait for your battery to charge!

Editor’s Note: You can use both of the above methods for charging your food truck battery with a generator as well.

Recharge time

The time it will take an RV battery to charge with a generator can really vary depending on the make and model of your RV and generator. It may be as quick as 2 hours or as long as 10 hours.

Another thing that can affect the recharge time is whether your battery is part charged, below 20% charged or completely flat. If it has very low power the charging can take a long time while if it is already at 70, naturally it won’t take as long to be topped up.

Can you charge a battery directly from shore power?

Actually yes, this is a great option for charging an RV battery. It is one of the most simple and most effective. In fact as long as you have a battery charger, you can use pretty much any 110 power outlet.

These are relatively inexpensive and easy to get hold of but it is recommended to invest in a smart charger, or three-stage charger. This is because they adapt their power output to match the power level of the battery so you don’t need to worry about overcharging your battery and causing damage.

This will really improve the lifespan of your deep-cycle battery as well as boost its performance.

Battery maintenance

So we mentioned this above, but battery maintenance is really important. How much maintenance a battery needs totally depends on the battery type. For example lithium batteries don’t need much maintenance at all while deep-cylce batteries do. Check the manufacturer to get the most accurate instructions but also follow these general rules.

• Keep your electrolyte levels flooded with water as the batteries lose water every time they are charged. You should use distilled water so that sulfur doesn’t form, otherwise known as sulfation, which is damaging to the batteries.
• Keep the battery terminals clean to help improve your battery performance and extend the shelflife. You can remove corrosion by mixing together baking soda and water and using an old toothbrush to scrub the solution on the terminals.
• Charge your batteries regularly, not letting them get too low in charge. Why? It helps them last much longer and provide more power each day if you keep them charged.
• Make sure you take care that you always attach the positive and negative cables to the correct terminals. How can you tell them apart easily? The red cable is the positive one marked with a plus (+) and the negative one is the black one marked with a minus (-).

Safety concerns to be aware of

There are a variety of safety risks that could present themselves when charging an RV battery. Therefore it is best to take all the necessary precautions to keep both yourself and your battery safe.

Cables and metal

As you will be moving and adjusting the battery cables, make sure the positive ones never come into contact with metal. This can allow electricity to flow into the metal which can be extremely dangerous if you touch this. It is also damaging for the battery.

Also never allow metal to contact the gaps between the two battery terminals. It can also be an easy mistake to make to absentmindedly attach the cables back to the wrong terminals by mistake. Double check before putting the cables back that positive (+) and negative (-) go back on the correct way when you are replacing them.

Battery car

As mentioned above make sure to keep check of the state of your battery. If the battery looks warped or cracked or has signs of damage, you should look to replace it as soon as possible. If you discover corrosion or a build up of dirt, make sure to clean this regularly.

This will not only preserve the battery’s shelf life but keep the battery as safe as possible for you to handle.

Keep it ventilated

Avoid charging your battery in an enclosed or covered space as the charging process can expel unpleasant and damaging chemicals. The battery itself may omit hydrogen gas that could be harmful when it builds up in a closed area.

The generator itself may produce carbon monoxide which is also dangerous and you should avoid coming into contact with it. Choose instead an open and ventilated area where these chemicals cannot build up over time becoming toxic.

Conclusion

So don’t fret, charging an RV battery using a generator might be tricky but just follow these simple steps and you shall always have power in your RV. Make sure you have all the correct chargers you need, the correct generator as well as the right tools and know-how to maintain your batteries with as much care as possible.

Make sure to follow all safety procedures as RV batteries can be dangerous when they are damaged or misused. Detaching and attaching cables from the terminals is also risky so take care. Overall, choose the method that works for you and make the most out of your RV. What adventure will you be going on next?