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Demystifying RV Batteries

By Jenn

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Battery life, capacity, voltage, series, parallel, amps, amp hours.

You might as well be speaking another language, right?

Let’s make it a little more simple for you, right now.

What does my RV battery do?

Your RV battery powers the 12v appliances and outlet in your trailer. In a T@b 320, that includes:

  • USB and 12v “cigarette style” outlets
  • Lighting
  • Jensen TV and stereo
  • Fridge (2021 T@b 320, 400 models with 12v fridge)
  • Fantastic Fan
  • Water pump
  • Tank and battery monitor
  • LP Monitor
  • Igniter for fridge on Norcold three way fridges (pre-2021 T@b 320 models)

In addition, the battery supplies a little bit of power to two propane powered appliances: the Alde furnace and hot water heater and the stove.

What can’t I use with only my RV battery?

The AC power outlets (standard household style), the air conditioner, and the microwave in the T@b require shore power, an inverter, or a generator to be used. On the T@b 400, equipped with an inverter, you may be able to use the microwave from the battery.

What do I need to run my AC from a battery?

Typically, you need either a generator or a very large solar array and very large battery bank to power an air conditioner. Can it be done? Probably. Is it worth it with a tiny towable? I don’t think so.

I typically choose a site with electricity when AC is absolutely necessary.

What is the battery provided by my dealer?

Your dealer will typically provide you with a 75ah to 100ah (ah = amp hour) wet cell lead-acid deep-cycle battery. Let’s break down what that means. These batteries are typically Group 34 size batteries.

A wet cell lead-acid battery is a traditional battery. It means that water levels need to be maintained in order for the battery to operate properly.

A deep cycle battery is typically used in boats and RVs. It differs from a starter battery, like the one used in your car, because they are designed to experience repeated charges and discharges without hurting the battery life.

The starter battery in your car is meant to retain a consistent level of current over a long period of time.

Amp hours are how you determine the capacity of a battery. a 75-amp hour battery is as small as you would want to choose for an RV.

However, with a lead-acid battery, you do not want to deplete it more than 50%. This gives you only about 35ah of usable capacity.

Generally, you will find that different amp hours, or capacities, are associated with different “group size” batteries. The standard dealer provided battery is usually a Group 34 size battery. A Group 27 battery (66 – 110AH) or a Group 31 (75 – 125AH) battery can sometimes fit into the same space with little or no modification to your storage space and give you a few more amp hours of capacity.

How long will my dealer provided battery last?

This is one of the most common questions a new RV owner face. There is not cut and dry answer to that question. How long it will last will depend on your camping style. If you are brand new to RVing, I recommend getting a feel for how you think you will camp. This post might help, too.

In addition to getting a little experience under your belt, you can calculate how much you would like to use the battery and estimate your power consumption against the battery capacity. I developed a spreadsheet to help you understand your power usage, here.

If you just need enough power to drive a few hours to the campground and plug into shore power, there, the dealer provided battery should suffice.

If you think you will be camping without electric, you may need to consider more capacity.

What are your options for improving off-grid capacity?

Watch this video to learn about the most common options.

How do I know what my battery state of charge is?

Your RV may come with a very basic battery monitor that gives you a number or even dots to show you what your current battery voltage is. The type of monitor that goes into a 12v outlet is similar.

These types of monitors are of some value, but they are more like checking a clock for the current time, than truly gaining insight into how much battery capacity is remaining.

If you do not much dry camping or boondocking. These methods may work perfectly fine for you.

If you get into dry camping or boondocking, you will want to consider installing a battery monitoring system with a shunt. I have ben suing Victron battery monitoring systems for several years and really appreciate the data they provide me.

The Victron BMV 712 provides a display and data to an app for your phone via Bluetooth.

The Victron Smart Shunt provides the same data but does not include an external display.

What are the different types of batteries available to me?

There are three type of batteries available:

  • Wet cell lead-acid
  • AGM (glass matt)
  • Lithium

Lead-Acid Batteries

As mentioned above, lead acid, have been the most common type used in RVs. Lead-acid batteries have retained their popularity because they are readily available and remain the least-expensive up-front costs for batteries.

Lead-acid batteries are heavy, and do not hold their charge well, especially in cold weather. They also require regular maintenance, ensuring that adequate water levels are maintained and are in general, more prone to corrosion. Lead acid batteries must be vented.

Lead-acid batteries cannot be depleted to 50% – below 12.06v you are starting to decrease your battery life. Depleting a lead-acid battery all of the way will lead to a very short battery life and it is easy to ruin your battery. It is not uncommon for a first-time RVer to ruin a battery because they deplete their battery accidently, or unknowingly, too far.

AGM Batteries

AGM batteries have gained popularity in both deep-cell and automotive uses, recently.

AGM batteries have become more popular because they are maintenance free, they can be used inside with proper venting, and there is little to no, “off-gassing” during normal use, thus less corrosion in the battery compartment.

They have not become more widely adapted because they are more expensive, heavier and slightly larger than lead-acid batteries.

You can usually deplete your AGM battery to about 40% before hurting your battery life and they tend to have longer life expectancies than lead-acid batteries. Some battery manufacturers claim you can go below that to 30% before it has a negative impact on life expectancy.

Why Do People Use Golf Cart (6v) Batteries?

Sometimes, you will see people using golf cart (6v batteries), in series. RV systems in the US and Canada are 12v systems. When you wire 6v batteries in series, the voltage is additive, so two 6v batteries produce 12v.

Golf cart batteries tend to have thicker plates, allowing more cycles and a longer life expectancy than typical deep-cycle batteries.

Golf cart batteries are available as either lead-acid or AGM types.

Golf cart batteries have been a common “go-to” solution for RVers for a long time. This solution provided a solid boost to capacity at an affordable price. The typical golf cart battery capacity solution provides around 225ah of capacity, thus providing about 112ah of usable capacity.

Can I run two 12v batteries in parallel to increase capacity?

Yes, you can run two 12v batteries in parallel to increase your capacity. This is a little less common, but perfectly acceptable. You won’t get the advantage of the thicker plates, thus prolonged life expectancy, that would get with golf cart batteries, but you will see expanded capacity.

Whether you choose lead-acid or AGM, there are many quality brands, but Trojan batteries probably carry the best reputation in the business. Of course, they are among the most expensive, as well.

Lithium Batteries

Lithium batteries are surging in popularity. Cost kept them out of the mainstream for a while, but the technology and competition have matured and are now a viable option for many.

They remain the most expensive up-front option and they are more complicated than lead-acid or AGM batteries.

Lithium batteries are smaller and lighter than either lead-acid or AGM batteries. They require no venting and are often installed inside of an RV. Additionally, lithium batteries can hold their charge for months, or even years and can be used to almost 100% of their capacity. Depleting a lithium battery does not decrease their life expectancy.

Some of the complexities of lithium batteries involve temperature and charging.

Lithium batteries cannot charge below freezing temperatures and are best stored inside during the winter but their lighter and smaller form factors make this easier to do.

Lithium remains expensive, up-front, but most believe their costs over the long term are actually less. Due to their recent emergence, this remains to be seen in practice, but the outlook is promising.

With the 12v fridge in the 2021 T@b 320 and my fondness for camping without electricity, I am have decided to upgrade to lithium batteries and will be installing two 100ah Lion Energy Lithium batteries. I chose Lion because they were smaller and lighter than other other lithium batteries and I was able to get a discount with a referral code.

If you decide to choose a Lion Energy battery solution, you can use my referral link to save 15% and I may earn a small commission from your purchase. The discount appears during the checkout process.

Charging Lithium or AGM Batteries

Both AGM and lithium batteries charge at higher voltages than lead-acid batteries. Every battery had a unique voltage profile, set by their manufacturer. Most RV converters, unless designated otherwise, do not reach the voltage needed to fully charge AGM or lithium batteries.

The inability to reach the proper charge probably has a bigger impact on AGM batteries because reaching the proper full charge has a better impact on AGM batteries. There is some emerging evidence that lithium batteries not only don’t suffer but might see enhanced expectancies by not fully charging every time.

There are some options for mitigating the voltage charge issue.

First, you could replace your converter. New converters design to support lithium or higher voltage charging profiles are available on the market.

Second, you can allow the solar controller to top off your battery. The Victron solar controllers used by nuCamp are designed to support lithium batteries. I have been doing this with my AGM batteries and it has been highly effective.

Third, you can use a smart charger. Smart battery chargers designed to support lithium are readily available and can be used to occasionally ensure that your batteries are receiving the proper charge. I have used this method, for years with both shore power and with my Goal Zero Yeti Lithium battery to recharge my T@b batteries. I simply plug the smart charger into the 120v outlet on the Yeti and then connect directly to the batteries on my T@b.

Charging from Your Vehicle Alternator

Vehicle alternators vary in how much they will supply to your trailer.

Newer vehicles with “smart alternators” especially, may suffer from lower voltages, particularly on longer trips. This can cause you to arrive at a campsite with less than a fully charged battery, especially when traveling a greater distance.

Some owners have improved this by running a higher gauge wire from the battery to the 7-pin connector or installing a DC – DC charger.

Get Charged

Hopefully, this has helped you start to get a grasp on understanding RV power. There is a lot to learn when you enter the RV world, so bookmark this and come back and read it again, and again. This post will be here.

What do you do?

Have you figured out what works best for you, yet? Let me know in the comments, below.