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All You Need to Know About RV Batteries

Don is a retired engineer and shares his experiences and knowledge with his readers to help them as technology gets more complicated.

A typical lead-acid battery for automobiles: how can you tell if an RV battery is bad?

A typical lead-acid battery for automobiles: how can you tell if an RV battery is bad?

All RVs Have Batteries

Yes, as an RV owner you know that all recreation vehicles will have batteries in them. Well, except for tents and other such simplistic weather protection gear. Of course, some tent users will carry their own pre-charged-up battery in order to provide power for the electrical devices they use when they go tent camping.

It is important that all RV owners and users understand:

  1. The basic battery applications used in an RV
  2. The location of each battery or battery bank in their RV
  3. The type of battery used in each location or application of the RV
  4. The age, size, and type of battery used in each location of the RV
  5. The method and equipment used to keep each battery or battery bank charging
  6. The methods to perform preventive maintenance on your RV batteries

1. Battery Power Systems Used in an RV

There are really only two electrical systems that use batteries in the typical RV and these would be the engine systems and the coach systems. Over the years, some RV manufacturers would use other names for these systems, but these are the most commonly used.

Some motorhome manufacturers build their own complete RV complete with a drivetrain that is usually referred to as a Class-A motorhome.

Other RV manufacturers will purchase a truck manufacturer’s chassis along with the engine/drivetrain, dashboard, and other operating equipment already installed and ready for the RV manufacturer to convert to a motorhome, and these are usually referred to as; Class-B, Class-B+, Class-C, Class-C+ motorhomes.

Essentially, the RV manufacturer would then mount their own camper/coach body along with all of the equipment that makes a camper a camper onto this pre-assembled chassis.

When talking about or explaining how things operate in their RV designs, these manufacturers will sometimes refer to the engine electrical system as being the “main” system, and rather than call the electrical system added by the motorhome manufacturer the coach electrical system, they will sometimes call it the “aux” system.

For the sake of simplicity, I will use the terms engine and coach in this article.

RV batteries are kept charged with the built-in converter (charger) of your RV. Many RVs will also have an inverter to generate 110-VAC from your batteries.

RV batteries are kept charged with the built-in converter (charger) of your RV. Many RVs will also have an inverter to generate 110-VAC from your batteries.

2. Coach Batteries and Engine Batteries Overview

Engine Batteries

The engine electrical system is the same as you would find in a standard truck from a truck manufacturer.

It will have typically at least one regular automotive lead-acid battery, and normally it functions as needed to support the electrical power needs of the truck electrical system even when it is used as the motorhome’s engine electrical system.

Coach Batteries

But the coach electrical system is often a much more complicated system as it must support the different electrical accessories and devices that were designed into the motorhome for the convenience of the RV owner.

Because of the differences in electrical equipment and electrical loads that these coach batteries must provide power for, the motorhome manufacturers will usually utilize not only multiple numbers of batteries, but also different types of battery designs.

At this point, I need to simplify things a bit, so for the rest of this article let’s assume that campers without their own engine/drivetrain—including travel trailers, fifth wheel trailers, toy haulers, and towable campers—will use some of the electrical systems that are just like the coach systems I describe, but often they will have fewer electrical equipments in them than with a large Class-A motorhome may have.

A RV motorhome on the road

A RV motorhome on the road

3. Where Is the RV Battery Located?

Before you go looking for a special compartment that is labeled “Batteries are Here," there are no standards for where an RV manufacturer might place the batteries. However, there are several economic limitations that force the manufacturers to place these power sources close to their power distribution boxes, fuse boxes, and such.

You see, large-diameter electrical wire, especially flexible electrical wire, is very expensive, and RV manufacturers will invariably place the battery compartments as close to these power distribution systems as possible.

The same goes for engine batteries, in that they will be placed where the truck chassis manufacturer had already placed them: in the engine compartment. Or as with a diesel pusher motorhome, the battery compartment will be as close to the rear of the RV body as possible.

It should be noted at this point that when you get to the different Class-B, Class-B+, and some Class-C+ motorhomes, the available space is so sparse that the RV manufacturers will often utilize any free space that they can find for their coach battery and their coach power and fuse block mounting sites.

So it is always important for the owners of these compact motorhomes to take the time to learn where these power control systems and fuse blocks are actually mounted before you encounter electrical problems.

4. Different Battery Designs Used in an RV

There are numerous different design technologies used in the manufacture of automotive-type batteries, which are by far the most popular physical style of batteries you will find to be used in RVs.

The battery technologies used in these batteries can be your simple standard Lead-Acid Battery design, or it could be one of the high-tech designs such as the less common Lithium batteries.

Lead-Acid Batteries

Most of the battery designs used in RVs today are referred to as lead-acid batteries. This is a simple battery design that has been used for over a century, and the most common battery-designed automotive voltage provided today is either 12-VDC or 6-VDC.

If you’re not a technical person, what this means is that the battery has several plates made of composite metal, usually, lead (often no longer used today). These plates are positioned inside the battery cavity and wired in series, parallel combinations with each other as needed to provide the necessary level of current for the RV.

The battery case is filled with a liquid mixture of acid and water, and this fluid allows for the flow of electrons between the plates, thus creating a voltage differential between the plates and thus between battery terminals.

When this type of battery is charged properly, it will retain a voltage differential between its terminals, and it can then be used to power electrical devices. Most of these batteries are simple designs and will usually give the user several years of reliable use.

However, there are some applications, such as marine boats, that will be subjected to high levels of vibration and will often even be fully discharged regularly.

A standard lead-acid battery will often break down under these more harsh physical conditions, and to avoid this users will want what are called deep discharge lead-acid batteries. These batteries are designed to be more rugged overall and they can take the abuse of being fully discharged and recharged, over and over without internal damage.

Distilled Water Only

NOTE: Lead-acid batteries get thirsty. By this I mean they have removable caps on the battery box, where you will need to occasionally add water when it evaporates from the battery; you should always use distilled water.

Do not use any other type of water such as drinking water, which will have minerals in it, because these minerals will build upon the plates inside the battery, and eventually cause it to not function properly.

You should also understand that your lead-acid battery use will reach a point where it can no longer provide a steady voltage, and if it is not then recharged properly, the voltage it provides will slowly drop, often causing numerous strange things to happen to your electrical devices in your RV that rely on a steady voltage source.

Lithium Batteries

We are all familiar with the battery design called a lithium-ion battery. We see these batteries used in our cell phones, as well as in thousands of portable devices that need a reliable, rechargeable power source, and most typically one that only needs to provide a small amount of power.

Recently, we see these lithium batteries being configured in a package similar to your common automotive battery.

One difference you will encounter when you decide to use one of these lithium batteries in your RV is the fact that they do not utilize any liquid chemical mixture that will need to be supplemented with more liquids in the future; they are resealed batteries.

Another difference is that, unlike your lead-acid battery, a lithium battery will provide a steady clean voltage output, right up to the point where it is fully discharged. In other words, it is designed to be fully ON or it will be fully OFF, without any drop in the voltage it provides.

Because of this function, you will get no warning such as; a fuzzy TV picture, or a ceiling light that is slowly dimming, or another such common indicator of what we are used to happening with a weak battery in your RV. As I have said, your electrical gear that uses your Lithium batteries will be ON or OFF, with no functionality in between.

NOTE: One thing the RV owner needs to consider if they want to use lithium batteries is that they will need to be prepared to pay a much higher price for these batteries as opposed to the standard lead-acid varieties they might be used to.

Other Battery Designs

I could mention the AGM battery designs and the spiral cell designs and other battery technologies that some RV owners are starting to use, but I’ll leave that discussion for another article.

Suffice it to be said that these are all complex designs of lead-acid technologies. Although they do function well for most RV owners, they also carry a significantly higher cost than the standard lead-acid batteries.

Charging RV Batteries

Your RV, if it utilizes batteries, will also have some type of charger (often called a converter) that is built into the RV. These converters are designed specifically for keeping your batteries properly charged.

They are usually powered by the 110-VAC in your RV that is provided by your 110-VAC electrical systems.

Always remember, that if you are traveling for days without any hookups, or if you are boondocking in the wilds of America, that battery charger needs to be kept powered on for it to keep your batteries charged.

Solar Chargers

Some RV owners will have one or more solar collector systems designed into their RV electrical systems.

Some of these solar systems will provide low levels of power to your batteries and they are designed to essentially just "trickle-charge" your batteries. This is when the battery voltage level drops below a certain point, it will sense this and turn ON to bring the battery voltage back up to a full charge.

These solar chargers are popular for use when your RV is kept in storage for long periods of time.

However, an increasing number of RV owners are having more complex and costly self-sustained solar electrical systems installed into their RVs. With these solar systems, the RV owners can travel further and for longer periods of time, often for weeks or even months, without having to return to campgrounds or other powered sites where they would ordinarily have to recharge their battery systems.

RV Battery Preventive Maintenance

Every RV owner should perform regular preventive maintenance on the batteries in their RV so that they can count on their batteries being operating at their highest efficiency.

Regardless of which of the battery designs I have mentioned your battery PM plan should include:

  1. Monthly: Remove the caps on your batteries and check the water level, and if necessary, refill the cells with distilled water,
  2. Monthly: Check the battery cases for cracks or leaks, often cause by vibrations, etcetera, while traveling; especially if you see battery acid residue in the battery compartment.
  3. Monthly: Examine all of your heavy wirings that are connected to your batteries and fuse boxes to make sure they are not loose or frayed,
  4. Monthly: Check that all of the clamps and straps that hold your batteries in place are in good condition and that the batteries will not move when you pull/push on them.
  5. Annually: Check the manufactured date on your batteries and if they are over 4-5 years old and you are planning on a long camping trip soon, you should replace them with new, fresh batteries.

The batteries in your RV really are simple devices, but so many RV owners tend to just forget about them when everything seems to be operating properly. And too often the case for most of us RV owners, we wait until things in the RV start to operate strangely, or not at all before we do anything.

So, a good RV battery PM plan can always help the RV owner stay ahead of these potential problems and continue to have a great camping experience.

“Nuff Said!"

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Don Bobbitt