How to Charge RV Battery with a Generator? (Quick & Safe)

How to Charge RV Battery with A Generator

There are a few ways to charge your 12V house batteries while boondocking.

Going green has its advantage, but you’ll be limited to when you can charge the batteries.

Thus, you need an on-demand power source like an RV generator to charge your house batteries.

So, how to charge an RV battery with a generator? The fastest way to recharge your house batteries with a generator is using the right size charger. A smart multi-stage charger can maintain the required voltage and pump enough juice to recharge your deep cycle batteries in no time.

In this article, we’ll take a look at the correct way to charge a 12-volt RV battery with a generator. Moreover, we’ll talk about alternative methods to recharge your RV batteries and answer some essential questions.

But before that, some basics about battery charging.

Do You Know: Your RV generator will not start if your battery is undercharged. Here you’ll find the most common reasons why your RV generator won’t start.

How is a Battery Charged?

No matter the type of 12-volt battery you have, they can be charged and recharged using a power source that is greater than 12 volts.

Usually, 120 or 240 volts.

In simple terms, the higher voltage pushes a lot of energy into the battery, thus charging it.

However, you’ll damage the battery if you continuously push too much power into it. 

To prevent it from happening, you need a high-quality smart charger to regulate the voltage at different stages of charging. While also converting the AC to DC power.

A smart charger will also keep a tab on if the battery is full and disconnect charging to prevent overcharging.

Note: Trying to charge your battery with AC power directly can increase the risk of battery damage, fire, and explosion.

State of Charge

The state of charge indicates how much charge is left in your 12-volt battery.

As your battery discharges, the voltage also falls. This can shorten the working life of the appliances using battery power.

While not the most accurate, using a multimeter is the easiest way to check the voltage. However, you can install an RV battery monitor to keep yourself informed about the state of charge on the fly.

Generally, the state of charge varies depending on factors like the type and brand of the battery, ambient temperature. Anything below 40 degrees can affect the state of charge.

The table below shows the voltage at different stages of the 4 most common types of RV house batteries.

Stage of ChargeSealed or Flooded Lead AcidGel BatteryAGM Battery
100%12.7+12.85+12.8+
75%12.412.6512.6
50%12.212.3512.3
25%121212
0%11.811.811.8

Keep in Mind: These readings are taken without any load and haven’t been under load for a few hours. You may have different readings depending on the load, and other factors discussed above.

Now, let’s look at a step-by-step guide on how to charge your 12 volt RV battery with a generator.

How to Charge An RV Battery with a Generator?

Technically, any type of RV generator (onboard or portable) can charge your onboard house batteries.

But the charging process is going to be very slow and inefficient.

Generally, batteries need Direct Current (DC) to charge, and most modern RV generators come with a 12V 8A DC outlet.

This is far too little power and will take ages to charge the battery fully while also increasing your fuel cost.

If your RV generator is using more fuel than usual, than have a look at the article on “How much fuel does an RV generator use“.

For example, a portable generator with a 12V 8A DC receptacle will take about 12-13 hours to fully charge a 100Ah battery.

The fastest way to charge a 12V deep cycle RV battery is to use a quality charger. A smart multi-stage converter charge is designed to convert the 120 or 240 AC to DC, driving more juice into the battery and reducing charging time.

Most importantly, these multi-stage chargers vary the amount of current going into the batteries depending on the current state of charge.

Here are the steps you should follow to charge your deep cycle house batteries safely.

  1. Park on level ground (use leveling blocks if necessary) and activate the parking brakes.
  2. Turn off the breaker that is bringing power from your battery bank into the coach. This will ensure your battery does not discharge when charging, increasing the charging rate.
  3. Now go to your house battery compartment and check to see any physical damage, corroded terminals, or damaged wires. You need to scrub and clean if you see sulfation (foreign colored stuff) on the terminals.
  4. Now it’s time to check the level of electrolyte in the battery. You need to be parked on level ground to find the correct level of electrolyte. If the fluid is low, refill it with distilled water up to its recommended level.
  5. If your battery bank is wired into your RVs 30 or 50 amp electrical system, turn off all the breakers other than the one that’s feeding the battery. This will ensure you have all the power from the generator going to the battery bank.
  6. Fire up the generator and let your smart charger do its work. Additionally, keep an eye on your battery meter to know the battery level and avoid unnecessary fuel burn.

This method will work with any type of RV batteries be it AGM, lead-acid, or lithium-ion batteries.

With the right size smart charger and RV generator, you should be able to charge your RV battery bank quickly.

Note: The ambient temperature below 40 degrees is one of many factors that can affect how much time it takes to charge your battery completely.

Alternative Methods to Charging your RV Batteries

The shortage of generator fuel is one of the few factors that may limit you from charging your RV batteries with a generator.

However, there are other ways to charge your 12-volt house batteries.

Some are green and don’t cost anything, while others may be dangerous and should only be used in case of an emergency.

In the end, you’ll find two methods of charging RV batteries that are not applicable for boondockers but are important to know.

Charge RV Battery Bank using Solar Power

Because of a long list of advantages, solar power has gained popularity amongst RVers and motorhome owners.

They don’t pollute the environment, make zero noise, and most importantly, produce energy for FREE FOREVER once installed.

Before you shop for your RV solar panels, it’s important to size your solar power system correctly. Additionally, you need to know the amount of available space on your camper roof to know how many solar panels you can fit.

You also have the option to buy portable solar panels if you have less space on your rooftop.

Solar panels convert the sun’s rays to electricity which then goes through an amp controller (aka charge controller). The charge controller measures the level of charge, controls the voltage, and prevents the battery from overcharging.

There are two main types of solar charge controllers to choose from:

  1. Pulse Width Modulation (PWM)
  2. Maximum Power Point Tracking (MPPT)

Among the two the MPPT charge controller is more efficient and advanced, thus it costs more compared to a PWM controller.

When sizing your solar charge controller, look for one that can transfer more wattage than your solar panels can produce. This way you have room to add more solar panels without having to buy a new charge controller.

The downside to using solar power to charge your RV batteries is, you’re limited by the weather. However, if you’re from the South West, you’ll love boondocking with solar power.

Note: Improper sizing of your solar charge controller may lead to a reduction of solar-generated power by up to 50%.

Charge RV Battery using Wind Turbine

Though less popular compared to solar power, there are instances when RVers choose to use wind turbines to charge their RV batteries.

A wind turbine uses wind power to rotate an alternator that produces electricity. This DC power goes through a charge controller, specially designed for smaller wind turbines.

Though producing electricity using wind energy is absolutely free once you have bought the turbine and the controller. 

However, wind turbines need a continuous flow of wind that may only be available in very open spaces. Else they will not be very efficient.

Wind turbines have a Maximum Wind Speed Rating that states the max wind speed they can handle before damaging themselves. So you shouldn’t drive with one installed on your RV.

Additionally, it may be illegal to drive with one since a wind turbine may break off your camper and injure people on the road.

Tip: With the right charge controller, you can use wind turbines and solar panels simultaneously to charge your RV batteries.

Charging RV Batteries using your Vehicle Alternator

Charging your 12-volt house battery using your vehicle alternator is a common practice.

Most modern RV’s are designed to charge their coach batteries this way when traveling.

When the engine runs, an alternator connected to the engine produces electricity. This power is primarily used to charge the 12V chassis battery and then your RVs house batteries.

If your RV is designed to use the alternator power to charge the batteries, it will automatically charge the house batteries when you drive.

However, not all RVs come with this facility by design. You need to check your specific RV model documentations to find out.

You can wire your RV to use the alternator power to charge the house batteries if your RV doesn’t come with it from the factory.

You can also use your tow vehicle’s battery to charge your camper’s 12-volt battery using a jump cable. It works with the same principle you would jump start your car with another car.

Just connect the black to black and red to red of your vehicle and house battery and fire up your tow vehicle’s engine.

This method possesses the risk of short circuit or worst fire if you do it wrong and should only be used if all else fails.

Overall, using your vehicle’s alternator to charge your house batteries is only efficient when you’re driving. Running your engine just to charge your house batteries should be avoided.

Charging RV Batteries using Shore Power

30 amp vs 50 amp RV plug

Using power hook-ups and other standard power outlets may not apply to people who strictly like to dry camp. Most importantly, they don’t apply to full-time RVers.

However, these methods are more geared towards weekend campers who don’t strictly boondock.

Generally, RV’s use either a 30 amp or 50 amp service depending on their size. The two services are very different in terms of power use and cables.

When your camper is hooked up to the shore power pedestal at the campground, it automatically charges your house batteries. While also powering your RV appliances.

The power from the pedestal enters the main circuit breaker that is then distributed to the appliances in the RV. The power from the battery breaker goes through a converter that converts the AC to DC power.

The DC power then charges the 12-volt house batteries.

A camper battery can also be charged using any standard 110 home outlet using the right extension cord. This works in the same way as hooking up to a 30 or 50 amp service.

So weekend campers also have an option to charge your house batteries from home before you hit your favorite campsite.

Undercharging and Overcharging your Battery

Undercharging and overcharging a battery consistently are two of the main reasons leading to a lot of battery-related problems.

Going dry camping with an undercharged battery means, you’ll run out of power sooner than you think. A faulty charger, lack of maintenance, and longer storage time are the most common reasons why your RV battery is undercharged.

Regularly undercharging your 12V battery will cause sulfation. Sulfation leads to the build-up of a coating of sulfate crystals on the battery terminals and plates. 

This lowers performance and the working life of the battery.

Tip: Deep cycle battery should never be discharged below 50%. Regular discharging to such low levels may lead to a dead battery. Use a battery maintainer if you plan to store it for long periods.

On the other hand, overcharging a battery has its own drawbacks. In deep cycle batteries, overcharging will heat up the battery plates and boil away the electrolyte solution (battery gassing).

Furthermore, the low water level will expose the plates resulting in the plates getting corroded.

Tip: Overcharging batteries are less common in RVs that use multi-stage smart chargers to charge batteries. These charges have a built-in monitoring system that cuts the flow of current as it is full.

To avoid damage from under and overcharging, you need to equalize your RV batteries.

In undercharged batteries, equalization eliminates sulfation by applying a higher voltage for a while. This should only be done by a trained professional.

However, the best way to equalize your 12 volt RV batteries is to use a smart charger. The smart charges prevent undercharging and overcharging, increasing battery performance and lifespan.

Keep In Mind: Battery equalization can only be done to wet cells or flooded batteries that have plates submerged in acid. It should never be done with Gel and AGM batteries.

Safety Measures to Keep in Mind while Charging RV Batteries

Whether charging an RV battery or working on any other electrical system, proper safety measures can prevent mishaps.

To begin with, wear safety gear like shoes, gloves, and goggles. Deep cycle batteries contain sulfuric acid that will burn anything it touches.

Lastly, use proper insulated equipment. When working with battery connections, you’re at risk of electrocution if you don’t have the proper equipment.

Following proper safety measures when charging or doing maintenance work on your RV batteries can prevent disasters and keep you away from harm’s way.

Related Questions

Can I charge my batteries with two different sources simultaneously?

Yes, you can charge your RV house batteries with multiple power sources at a time.

You can use power from your generator, solar panels, wind turbine, and alternator. You just have to use the right smart charger and charge controller to prevent overcharging and undercharging issues.

However, there is no charge controller if you’re going to use a jumper cable to charge the house batteries. This can lead to overcharging and excessive gassing leading to other problems.

What size generator do I need to charge my RV batteries?

The size of your RV generator has nothing to do with how fast your coach batteries will recharge. It all depends on your battery charger, especially, how many amps is your battery charger driving into the batteries.

A 12,000-watt generator will not charge any faster than a 2000 watt generator if your charger outputs lower amperage.

Buy a higher amp smart charger, especially a multi-stage charger with a high amp output. You don’t have to worry about the generator size to charge your batteries.

Check our post on how to choose the right size RV generator whether you have a 30 amp or 50 amp RV.

Conclusion

By now you know how to charge an RV battery with a generator correctly. The size of your generator doesn’t matter, all you need is a right-size multi-stage smart charger.

And this is the fastest way to charge RV batteries.

Alternatively, you have the option to go green with solar and wind turbines to charge the coach battery. Plus, you can use your tow vehicles or motorhomes alternator to charge while driving.