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How To Charge Battery with Generator?

Home and Portable Generators come in handy when there is a severe power outage due to natural disasters, grid failure, or any other reason. Depending on your situation, you can create a permanent standby setup and hardwire the generator to your residential electrical system or use the generator as a true “portable” one by using the outlets of the generator with good quality extension cords. While powering small to medium electrical devices, appliances, and tools with the help of a generator is quite common, a strange thing that often many generator owners think about is how to charge battery with generator.

This is especially true with people who are using generators with their motor homes (RVs or Camping Vans). Other similar situations where people want to charge their batteries with the help of a generator are home backup systems, car batteries, etc.

If you are in a situation where your RV battery, Car Battery, or other similar backup batteries are drained and you want to charge them using a generator, then you will have so many questions and doubts.

Don’t worry. This guide is just for you. Here, we will understand the basics of battery charging and also how to charge a battery with a generator. In the process, we will see answers to some important questions.

Battery Scene in Automobiles

Batteries are an important part of our lives, be they large or small. Let us focus on the large batteries for this discussion. Where do we use large batteries? The first thing that comes to mind is our vehicles (cars, trucks, motorbikes, etc.).

In Cars

Let us not discuss EVs (electric vehicles) and Hybrid Vehicles but only cars with good old internal combustion engines. The main purpose of batteries in cars is to start or crank the engine.

Although once the car engine starts and the alternator in the car recharges the battery it might not be sufficient to fully recharge it. This is okay if you take your car out regularly.

But if you park your vehicle for a long time, then the level of discharge of the battery will be severe and it might not even start the car.

In RVs

Another popular application of batteries is in RVs. Similar to cars (and other vehicles), even RVs have a regular Starter Battery to crank the engine (but with slightly different specifications).

In addition to this, there is another battery (or a set of multiple batteries) in RVs. The purpose of this secondary battery (or batteries) is to supply electric power to different parts of the RV or Motor Home so that we can use several devices and appliances (just as we use them in our homes). As a result, we sometimes call these batteries House Batteries.

These batteries cannot crank the engine. Other specifications and parameters of these batteries are also different from regular Starter Batteries of RV.

The Starter Battery (more commonly known as SLI Battery, which is short for Starting, Lighting, and Ignition) in an RV has the advantage of being charged by the alternator as soon as its engine starts. But this is not the case with House Batteries of RVs.

While they provide energy to different appliances in an RV, there is no normal way to automatically recharge them. You need to take the necessary steps to charge these batteries with proper charging systems, power supplies, etc.

Some RV owners design the RV’s electrical system in such a way that when they plug the RV into a 30A or 50A outlet in RV Parks, a special charger in the RV will recharge the house batteries.

Alternatively, some RV owners design the electrical system with a built-in generator. There is no need for making any connections or wiring as the generator is already a part of the electrical system. They simply have to start the generator and it recharges the batteries automatically. This way, you don’t have to rely on the grid.

Purpose of Batteries in RVs

What if you don’t have a built-in generator? How to Charge the Battery with a Portable Generator? Before answering these questions, let us take a quick look at the actual purpose of RV Batteries.

We already covered briefly about this topic in the previous section. But the purpose of a Starter Battery in RVs is to, well, Start the RV’s engine. Additionally, this battery also provides energy for lighting, ignition, radio, and other cabin requirements.

Next, we have the Secondary Battery System in RVs, which we normally call the “House Battery” as it is the main source of energy for different electrical appliances in the RV.

Speaking of electricity in RV, a quick reminder on different ways you can get an AC Mains supply inside an RV. There are three ways you can get 120V 60Hz AC Power inside the RV. They are:

  • Shore Power (by plugging in the RV’s Electrical System to a standard 120V Outlet or other dedicated RV outlets)
  • Generator (either a built-in one or portable one)
  • Inverter with a lot of Batteries

Of the three, plugging in the RV to the grid (if your RV’s electrical system supports it) is simple, easy, and of course, cheap. But the problem with this system is you need to park your RV to use the power.

This is where the other two systems come in handy. The first is the generator. You can build the electrical system of your RV with a built-in generator or use it with a portable generator.

Additionally, you can install several Deep Cycle Batteries in the RV, hook them up with a power inverter, and access 120V AC Power inside the RV, even when you are on the go.

The combination of batteries and generators can be even more exciting. You can run appliances off of the battery (in combination with the inverter) and use the generator only to recharge the batteries or supply energy when you parked the RV.

Irrespective of the source of power, their main purpose is to provide AC Main Supply at the outlets in the RV. This way, you can run different appliances such as refrigerators, coffee makers, electric stoves, TV, lighting, etc.

Why do RV Batteries Die?

It is clear that batteries in RV are very important if you want a proper off-grid living experience. As you use the batteries to power different electrical and electronic appliances, they gradually discharge.

If you continue to use draw power from the batteries like that, they will eventually go flat.

Even if you don’t use the batteries, there is a chance that they lose their charge. This can happen if you don’t take your RV for a long time. In this scenario, both the starter battery and the house battery will be completely discharged.

Weather, especially cold weather, is also a problem for batteries. If you live in a cold region, then the rate of discharge is significantly more than in other regions.

Irrespective of the reason, you have to properly take care of your RV Batteries to get maximum performance from them for a long time. The first step in this is to regularly recharge the batteries.

Preparing to Charge Battery with Generator

There are several ways to recharge an RV Battery. But if you are on a camping trip or don’t have access to shore power, then what are the possible ways to recharge them?

This is where portable generators come in handy. Can we directly recharge the batteries using a generator? No. you cannot simply connect the batteries to the generator and expect it to recharge. Please don’t do this. This is extremely dangerous.

Batteries are DC Electrical systems i.e.; they supply DC Power. In order to recharge them we need a proper DC Charging System. The output of the generator (usually) is AC.

Even though some generator models come with 12V DC Ports, these are not designed to recharge Batteries.

A brief reminder on battery voltage. The majority of batteries we use, be it Starter Batteries or House Batteries, are 12V Batteries. The Starter Batteries are usually of Lead-Acid type or sometimes Gel type.

But the “house” batteries are usually a special type of battery known as Deep Cycle Batteries. You can get deep cycle batteries as lead-acid, Gel, or Lithium types.

Regardless of the type, all these batteries are usually 12V and in order to charge them, you need to supply 13.5 to 14.5V DC. Again, just providing this voltage to the battery might not do any good.

You need a special circuit (equipment) that constantly monitors the voltage of the battery, sets the rate of charge (amount of current going into the battery), and other important factors.

We simply call these devices “Battery Chargers”. Again, there are different types of “chargers” such as smart chargers, fast chargers, multi-stage chargers, float chargers, trickle chargers, battery maintainers, etc.

The type of battery (lead-acid, gel, lithium, etc.) also determines the battery charging system and essentially the type of charger you use.

So, check the type of battery you have, get a suitable charger, and you are ready to charge.

How to Charge Battery with Generator?

The procedure for recharging RV Batteries with the help of generators involves using the 120V AC Outlet of the Generator. We have to plug the Battery Charger into this outlet and then charge the batteries.

If you have a large set of batteries, then you can get a 240V Charger (a battery charger that plugs into the 240V Outlet of the generator) as it can supply large currents (20A or more). In this case, make sure your generator can output 240V.

4 Steps to Charge Battery with Generator

Here are four simple steps you can follow to charge your RV Batteries with the help of a Generator and appropriate Charger.

Turn On the Generator

Place the generator on a relatively flat surface and check if you have the necessary fuel (gasoline, natural gas, or propane). If everything checks ok, then start the generator and let it run so that the engine warms up. This way, you can ensure that the engine is at an optimum speed and the output voltage is stable.

Connect the Battery Charger to Battery

Next, we have to connect the battery charger to the battery. Every battery charger comes with two clips (alligator clips or something similar to clamp onto the terminals of the battery).

One clip is red while the other is black (this color coding is also universal). If you are familiar with DC Electrical Systems. Then you will know that red is almost always positive and black is negative.

So, connect the red clip to the positive terminal of the battery and the black clip to the negative terminal of the battery. These terminals will sometimes have similar color coding but definitely have ‘+’ and ‘-’ markings.

Plug the Charger into the Generator

Once you are certain that everything is connected properly, you can go ahead and plug the battery charger’s power cord into the AC Outlet of the generator and switch it on.

Depending on the type of charger you have, it will either automatically shut off after fully charging the battery, goes into trickle charging mode, or something else.

Check for the indication on the battery charger as it most certainly will show a full charge indicator.

Disconnect Everything and Turn Off the Generator

Once the battery is fully charged, you can turn off the charger and disconnect it from the terminals of the battery. First, remove the black (negative) clip and then remove the red (positive) clip.

If you have other batteries, you can recharge them using a similar procedure. Once all your batteries are fully charged, you can turn off the generator.

Additional Information

The amount of time it takes to fully charge a battery depends on multiple factors such as the state or level of discharge of the battery, rate of charge (ampacity of the charger), etc.

For example, if you have a 12V 100Ah battery and you charge it with a 12V 20A Charger, then it will take approximately 5 hours to fully charge a completely flat battery.

But if the battery is only half discharged, then it will take only a couple of hours to fully charge it.

Another important thing you need to take care of is the level of electrolyte in the battery, particularly for flooded lead-acid batteries. If the electrolyte level is low, then you need to add distilled water. Take necessary precautions while working with batteries (of any kind).

You can also charge the starter batteries of your vehicle (car, RV, etc.) using a generator (and obviously a battery charger). If you have an off-grid setup in your home or cabin and rely on batteries, solar, and/or a generator, then you can recharge those batteries with the help of a generator.

If you have a solar charging system, then generators come in very handy during winter as there won’t be much sunlight. You can charge the batteries using portable generators so that they won’t go completely flat or die (which is actually bad for the batteries).

If you are looking for a generator just to charge RV batteries, then you don’t need a super powerful and expensive generator. Any small generator that can output 600 to 1,000 Watts of power is more than sufficient.

However, if you plan to run appliances in your RV off of your generator, then you will need a slightly large generator (something like a 5,000-Watt or 7,500 Watt generator).

By properly charging and maintaining the batteries, you can expect them to serve you for a long time (usually between 5 to 7 years).

Also Check: How To Charge Your iPhone Without a Charger


Batteries are one of the simplest sources of power. We use them in our cars, RVs, homes, and many other places to start our engines, power devices or appliances, etc.

In RVs, batteries have two purposes. One is to start the engine of the RV and the other is to power different RV appliances. As both these applications are different, we have two types of batteries for respective jobs.

Regardless of the type and purpose of the battery, they get discharged as you draw power from them and you have to charge them regularly.

Charging batteries, especially RV Batteries, can be challenging if you are not prepared for it. For a truly off-grid experience, you can carry a generator as it can provide power to your RV’s appliances and at the same time you can charge the batteries.

In this guide, we saw the basics of batteries in RV, their purpose, and the factors that make the battery die. After that, we saw how to charge battery with generator and also all the associated steps.

We hope that this guide could help you understand the basics of charging RV batteries using a portable generator. If you feel we missed something or want us to add anything, do let us know in the comments section. It will not only help us but even other readers.

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