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Charging RV Batteries Correctly: How to Charge Batteries the Right Way


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Camping With Power

Outdoor camping remains one of the most popular recreational or vacation activities in the US. It has spawned a 587 million dollar industry that serves more than 40 million participants each year

But you may, along with many others, find it hard to truly immerse yourself in nature without a few of the modern conveniences that society has grown accustomed to. These include microwaves, electric heating and air conditioning, and hot water showers.

All these of course require electricity to run. Your motorhome delivers this through carefully engineered deep cycle batteries.

Differences Between Your RV Battery and a Car Battery

You might think that motorhome batteries and car batteries are similar. It’s true that car batteries and RV batteries are both 12 volts. The important difference, however, is in the manner in which they’re used, and as such how they are charged also is a different process. 

Lead Acid Wet Cell Deep Cycle RV Battery Diagram

Car batteries are only used to provide the short and powerful energy burst necessary to start the gas engine. Other than that requirement, car batteries perform a few other minor functions that are typically low-voltage, such as powering the radio or operating the power windows.

An RV battery has a much greater responsibility. It powers the vehicle’s appliances, such as cooking appliances, water heaters, refrigerators, or even clothes washers and dryers when the vehicle is not connected to the power grid (known as dry camping).

Charging your motorhomes batteries should be routine after discharging 50 percent of the battery. While your car battery is also continually being recharged by the car’s alternator, fully discharging the car battery and recharging, it will drastically reduce the battery’s lifetime and efficiency. 

Battery Ratings

RV batteries are rated in four different categories:

  • Cold Cranking Amps (CCA).
  • Cranking Amps (CA).
  • Reserve Capacity (RC).
  • Amp-Hours (AH).

Cold Cranking Amps is the measured current that batteries can produce in cold weather. It’s measured at 0 degrees Fahrenheit and must provide a consistent current for 30 seconds without dropping below 7.2 volts.

CCA is an important rating to ensure that your RV or car battery can turn the engine in freezing conditions. Without this guarantee, it’s likely that your motorhome might not start during cold winter mornings at a campsite, or even worse—in the wilderness.

Cranking Amps, also known as Marine Cranking Amps, are measured at 32 degrees Fahrenheit. This is a much more common temperature condition for starting the engine or for powering RV appliances.

Reserve Capacity is the length of time that a battery can discharge 25 amps before the voltage drops below 10.5 volts. As you might imagine, the battery voltage slowly decreases as the energy capacity is discharged. 

It’s essential for your battery system to maintain a high voltage in order to power many of the RV appliances. This is why the RC rating is important, because low-voltage batteries may fail to operate crucial electrical equipment, or worse, damage certain appliances.

Pro-Tip: If you get fed up testing your battery capacity with a volt meter, consider investing in a battery monitor. These devices will give you an up to date read-out on the health of your RV battery system.

Perhaps the most important rating for a battery is the Amp-Hour rating. AH is a measure of the total energy capacity of the battery. 

Amp-hours are calculated by multiplying the amps drawn from the battery by the amount of time that the battery can provide that current. For example, if a battery can deliver 10 amps for 10 hours, its rating would be 100 AH.

This is the most important number to understand when considering your recreational vehicles electrical demands. You will want to calculate the AH requirements of your most commonly used appliances and make sure that your battery is rated highly enough to meet those demands overnight.

The Basics of RV Battery Charging

How Batteries Are Charged

Deep cycle 12-volt batteries are charged when they are connected to a power source with a voltage greater than 12 volts, usually 120 or 240 volts. This drives a powerful current through the wet cell and polarizes the internal lead plates that store the charge.

Of course, a greater current will charge the batteries more quickly. This is why camp power pedestals stations usually provide 30 or 50 amps, compared to your home’s 15-amp outlets. These additional amps can also power the multiple electrical appliances in your RV while charging.

State of Charge

“State of Charge” refers to the level of energy (in percentage of amp-hours) remaining in the deep cycle battery. As the charge decreases, the battery’s voltage will also gradually decline. As mentioned in a previous section, this decrease in voltage can negatively impact your RV’s electrical performance.

Below is a table showing the voltage drops at various states of charge:

These values are taken when the battery isn’t currently being used. If there is a current draw on the battery, these voltages will drop even further.

How to Charge Deep Cycle Batteries (Step-By-Step)

In some cases, you may need to charge the battery directly. These steps will help you safely restore power to the battery.

  1. Make sure you’re parked on level ground and set the parking brake.
  2. Turn off the engine and all internal appliances. 
  3. Locate the battery or batteries (the motorhome may be powered by batteries connected in series or in parallel, and each battery should be charged separately).
  4. Using a wrench, remove the cables from the battery leads. Remove the black cable from the negative terminal first, then the red cable from the positive terminal.
  5. If there is any sulfation on the terminals, scrub them clean with a wire brush and a paste made of baking soda and water.
  6. Check the water level and refill with distilled water if necessary.
  7. Attach the converter (or battery charger) cables to the battery in reverse order (red/positive first, black/negative second). The converter is necessary to convert the 120-volt AC power source into a 12-volt DC power for the battery.
  8. Plug the power converter or charger into the power source and turn it on from the switch panel or circuit breaker.
  9. Your converter or charger usually has an indicator light to inform you that the battery is fully charged. At this point, turn off the power and disconnect the battery by performing these steps in reverse order. Undercharging can lead to sulfation, and overcharging can also reduce the lifespan of your battery, so ensure you keep an eye on it.

These instructions are the same whether you need to know how to charge the house battery from generator, shore power, or using solar panels.

Furthermore, if you’re wondering, “Does the RV battery charge when plugged in?” Whether you’re connected to shore power using a converter or a battery charger, it will charge the battery. The only difference is that the converter will also power your RV’s appliances.

Don’t worry about how to charge your house battery from the vehicle, as this should happen automatically as you drive your RV.

What Happens If You Undercharge or Overcharge Your Batteries?

When charging your travel trailers power system, it’s important not to undercharge or overcharge the battery. In this section, we’ll explain the reasons why. We will also provide helpful tips to avoid undercharging and overcharging and to charge your battery to the necessary levels correctly.

Undercharging Your RV Battery

The main risk that you run from undercharging your RV battery, of course, is that you will run out of battery power sooner than expected! This can leave you stranded in nature without lights or heat, and might even prevent you from starting your engine.

This is also an appropriate time to mention that your deep cycle RV battery should rarely, if ever, be discharged to less than 50 percent of capacity. If you frequently drain your battery below 50 percent, this will reduce the lifespan of your recreational vehicles battery.

sulfate crystals on deep cycle lead acid battery

If you undercharge your batteries, it’s also likely that your battery might be stored for long periods with a low charge. Storing them with a low charge causes sulfation, which is the formation of sulfate crystals on the terminals and plates of the battery. Sulfation is one of the leading causes of unit failure.

There are at least a few ways that your battery might end up in a low-charge storage situation. If you leave your battery in your motorhome, then parasitic drainage might occur.

Parasitic electrical demands come from those very small electronics that don’t consume much power, so they are easy to overlook. However, they are constantly using power, and because they are overlooked, they can significantly drain your battery over long periods of time. Examples of parasitic loads would be your clocks and warning lights.

The best way to prevent parasitic draining is to remove your battery from your RV during long periods of disuse. However, even when sitting on a shelf, your battery will self-discharge. You might leave your battery alone for several months and return to find its terminals completely corroded with sulfation.

The best way to prevent low-charge storage problems is through regular (i.e., monthly) use of your RV. Not only will this prevent sulfation, but this will provide you with the enjoyment that you originally purchased your RV for.

Pro-Tip: When you go to charge your batteries do a quick health check on them and a little maintenance. Fill any low water levels with distilled water and clean any residue or corrosion off the battery terminals (or casing) with a mixture of water and baking soda. Always wear gloves, closed toe shoes and safety glasses to protect yourself against battery acid.

If you don’t have the freedom or the time to use your RV every month, you should remove the battery when not in use, and check the charge on a monthly basis. Typically, your battery will require a top-up charge every three months.

Alternatively, you can buy a battery maintainer, often called a Battery Minder or Battery Tender. These chargers will provide a trickle charge that will keep your battery full without overcharging.

Overcharging Your RV Battery

This leads us to the problems of overcharging. Consistently overcharging can reduce the lifespan of the battery cells and lead you to early and expensive battery replacements.

Inside your RV battery, lead plates are suspended in an electrolyte solution. Once the battery reaches full charge, the charging current can begin to electrolyze the water in the solution, separating it into hydrogen and oxygen gas. This gas can easily escape the battery casing, lowering the electrolyte levels and exposing the plates, causing further malfunctions.

Not only is this electrolysis harmful to your batteries, but the combination of hydrogen and oxygen gas is highly flammable. It’s possible that any sparks from the battery or charging system could lead to a small but dangerous explosion if your work or storage area is not adequately ventilated.

This is actually the most easily mitigated danger, and you can prevent electrolysis problems by making sure your area is ventilated and routinely refilling your battery with distilled or deionized water.

However, there are more severe problems associated with overcharging your battery bank, especially for long, unmonitored periods. The constant current delivered to the batteries can cause them the temperature to rise, which might warp the plastic casing. If this breaks the integrity of the casing, the batteries acid might leak, and the battery will become unusable.

Equalizing Your RV Battery

For all of the reasons mentioned, it’s critical to make sure your batteries are charged to its precise capacity. Many “smart chargers” on the market will do this automatically without the dangers of undercharging or overcharging your RV battery.

Another method you can use to extend battery life and improve your batteries performance is through regular battery equalization. Battery equalization is the process of overcharging the batteries by 10 percent to equalize the voltage across the internal plates. 

Equalization can eliminate sulfation and reverse another problem called acid stratification. This process should only be done by a professional, and only about twice a year.

Methods to Charge Your RV Batteries

There are several charging devices or methods available to you:

  • Alternator charging.
  • Hooked up to shore power (using a converter)
  • Plugged into shore power (using a RV battery chargers).
  • Generator charging.
  • Solar panel charging.
RV Electrical System

Alternator Charging

If you’ve ever wondered how to charge recreational vehicles batteries from your vehicle, it’s not complicated. In fact, charging your batteries can be done automatically by the alternator while driving. The alternator converts the mechanical energy of the engine into usable electric energy to store in the battery. 

There is one caveat to this though – not all RVs facilitate this. So have a good check of your RVs documentation first.

If, however, it does, and you’re planning a long road trip (more than 300 miles) before camping, you’ll almost certainly arrive at your destination with a fully charged battery. However, running your engine idly to charge the batteries is not the most efficient choice.

Shore Power Charging (With a Converter)

However, if you’re planning more than one night at your camping destination without any long-distance driving between nights, you’ll need a secondary method to ensure your house batteries are fully charged. 

If you’re lucky, your campsite will have electrical hook-ups for to charge your battery bank (this will certainly be advertised on location and also on any campground websites). Typically these camp pedestals will have a variety of outlets to suit your campers cable and plug. 

A campground power pedestal will usually provide electricity at either 240-volts or 120-volts, and at either 50-amps or 30-amps. As a comparison, your home electrical outlets are 120-volt and 15-amps. All municipal power is alternating current (AC).

Since most of your RV appliances are designed to run from your 12-volt DC battery, you will need a power converter to step down the shore power voltage from 240-volts to 12-volts, and also to modulate the alternating current into direct current (DC).

The converter is great for charging your recreational vehicles batteries while also powering your recreational vehicles appliances. But you should look for a converter that has surge protection because electrical storms can cause power surges in campground pedestal that can damage or destroy your RV electrical system.

Shore Power Charging (Using a Battery Charger)

Many new rig owners ask, “Does my RV battery charge when plugged in?” The answer is simply, “Yes.” A more important question would be, “Will my RV appliances function when plugged in?”

With a converter, the answer is “Yes.” Connecting your travel trailer directly to shore power stations using a converter will charge your deep cycle lead acid batteries while also providing 12-volt DC power to your RV electrical system.

A battery charger, unlike a converter, will only charge the recreational vehicles batteries without powering your RV appliances. When you are using a battery charger at a shore power pedestal, you should turn off most of your power-demanding internal appliances. Even smaller electronics, such as light bulbs, can divert the current that you need to charge your battery.

Whether you’re using a converter or a battery charger, you should also include a surge protector to prevent your camper from electrical damage in case of overload. Thunderstorms are much more dangerous for campers than they are for city dwellers because most homes and buildings have some kind of lightning protection built into their construction.

Generator Charging 

But what can you do if you’re truly journeying into nature, away from the conveniences of campsites and their electrical hook-ups? You can always drag along a generator and some extra fuel, and this is a reliable way to stay charged.

However, battery charging with generators is often noisy and cumbersome. Their presence could detract from your enjoyment of the peace and solitude of nature.

Solar Panel Charging

It’s become popular for some campers to choose renewable energy to recharge their AGM batteries, such as the use of solar panels or wind turbines. Although this may not be as reliable as other methods, it’s perhaps a cleaner and more environmentally-responsible method.

The downside to charging your batteries with solar panels, is primarily, that you are a hostage to the weather. If you’re boondocking down in the south west where solar power is a pretty reliable power source then no problem. Charging a battery bank with solar panels may be trickier in more northerly climbs.

The other consideration is how big a solar panel array you have versus your rigs power consumption. Your house batteries may drain faster than solar charging can replenish them if this equation is tilted towards the consumption end.

Lastly, a solar power setup can become a quite involved precess, as you will need various other pieces of kit like a charge controller to help regulate the amount of current and voltage being delivered to your power system. That said, if your camping lifestyle is more attuned to off grid RVing, then they can make a lot of sense.


There are several measures you should take while handling and charging your batteries to prevent unexpected danger.


1. Wear safety gear, such as eye protection, gloves, and long-sleeved clothing. Batteries contain sulfuric acid, which can burn clothing and skin, or cause respiratory tract and eye irritation. Furthermore, connecting the battery leads will often result in sparks. It’s always best to cover your skin and eyes in these potentially dangerous situations.

2. Never lean directly over the unit when changing or charging. As mentioned in the first point, sparks can jump from the battery, so keep your face clear. Additionally, the battery (not to mention the engine) can release hazardous fumes that you don’t want to inhale directly.

3. Make sure the work area is well-ventilated and never near a gas pump. This goes back to the hazardous fumes we just mentioned. Your motorhome is probably parked outside, but it’s always best to consider this necessary precaution.

4. Tighten gas and vent caps first. If the unit is going to spark, you definitely don’t want any escaping gas fumes that could potentially ignite.

5. Use the proper equipment. Properly fitting wrenches are best, but an adjustable wrench is still safer than pliers. A wire brush and a weak solution of baking soda in water will help remove sulfation around sulfation before you being to charge.

Running at Full Power

If you follow these steps for battery charging and storage, along with all the provided instructions that came with your batteries, you’re sure to enjoy many worry-free trips with your camper for years to come.

We hope that you enjoyed the information in this tutorial. Keeping your rigs batteries charged and maintained will give you peace of mind when you next go camping. If we can provide peace of mind to our readers, then our mission is complete.

Please leave a comment if you have any further questions or even advice to share with our community. Share this article among your camping friends and family to help them with their deep cycle batteries as well!

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