Wondering whether 6V or 12V batteries are better for your RV?

I don’t blame you for asking – and I don’t blame you for being confused, either. Most of the blog content written on this question is shockingly bad and inaccurate. And most of the “campfire talk” around the issue isn’t much clearer.

Let me assuage your anxiety. Either solution will work. There is no WRONG answer. Please do not spend hours online searching for the “perfect” solution. Life is too short for another internet rabbit hole.

Here’s the spark notes answer: Many RVers who are serious about dry camping will use two 6V golf cart batteries connected in series. This has very little to do with electrochemistry and much more to do with the fact that 6V deep-cycle batteries tend to be easier to find and less expensive than their 12V deep-cycle equivalents. It’s a market question, not a science question.

However, the advent and advantages of lithium batteries will soon, I believe, take over both batteries.

Here’s an example of two 6-volt deep-cycle batteries in a motorhome house battery bank. It’s not magic, I promise.

Welcome to RV Battery Chemistry 101

Before we dive deeper into this topic, here are a couple of things you need to understand about your RV’s electrical system.

As you probably know, your RV has both a 120-volt AC (alternating current) electrical system and a 12-volt DC (direct current) electrical system.

• The AC system runs larger appliances like microwaves and air conditioners
• The DC system runs smaller loads like lighting, water pump, TV, etc.
• Converters and inverters are a bridge between the two systems.
• AC power comes from plugging into the grid or a generator.
• DC power comes from the house batteries (which is our subject today).

Got all that? Now, let’s establish some basic facts about your house batteries.

For years, the standard RV house battery was a lead-acid battery. AGM, sealed, flooded, VRLA, wet – these are all types of lead-acid batteries. The newcomers on the block (and my personal favorite) are lithium iron phosphate (LiFePO4) batteries, which offer about 4x the energy density.

Batteries are normally rated by voltage and amp-hours. The number that most accurately calculates the useable power in a battery is actually watt-hours, which is volts x amp-hours. 

Examples:

• A 12V, 105Ah battery has 12 x 105 = 1,260 watt-hours.
• A 6V, 208Ah battery has 6 x 208 = 1,248 watt-hours.

So don’t get distracted by comparing amp-hours. The only way to compare the stored power of a battery is the watt-hours. 

Also, the energy inside batteries varies with how fast you discharge them. You can only pull energy out of a battery so fast. Generally, the faster you drain a battery, the less energy you’ll squeeze out of it (Peukert’s law). Most RV house batteries should be discharged between a C/3 and a C/20 or slower rate (3 to 20 hours). 

Here’s a visual image I find helpful: Imagine trying to take a shower by dumping a 5-gallon bucket over your head versus standing beneath a showerhead sprayer. The showerhead is slower, but you’ll clean yourself better! In the same way, slower battery discharge is often more effective.

Lastly, batteries can be connected in two ways: series and parallel (or a combination thereof).

• If you wire batteries in series, you increase the voltage, but the amp-hours stay constant.
• If you wire batteries in parallel, you increase the amp-hours, but the voltage stays constant.

Think of connecting two Lego blocks. Stack them, and they’re taller, but no wider. Lay them side-by-side, and they’re wider, but no taller.

So if you want to use 6V batteries in your RV, then you have to wire two 6V batteries in series to equal 12V total. (We’ll talk more about this in a minute.)

Are 6V Golf Cart Batteries Better than 12V RV/Marine Batteries?

There’s nothing inherently magical about a 6V battery that makes it last longer than a 12V battery. Voltage doesn’t determine durability. The two have nothing to do with each other.

So, where did this myth spring from? Well, it’s a problem of false equivocation.

Here’s a basic fact: You can’t design a lead-acid battery to do everything. You have to choose between a battery designed for rapid discharges or deep discharges. You can either be a sprinter or a marathon runner – not both. 

Now, most RVs are supplied by the dealership with an RV/marine 12V battery. A marine battery is a jack-of-all-trades battery, somewhere between a starting battery (like your car) and a true deep-cycle battery (like a solar battery). Unfortunately, it only takes a few deep discharges (50% or below) to severely shorten the lifespan of a marine battery. So somehow people started equivocating marine batteries with all 12V batteries, and now 12V batteries have a reputation for being less durable. 

What about 6V batteries? Well, the opposite has happened. Some of the most common applications for 6V batteries are golf cart batteries, solar bank batteries, and uninterruptible power supplies (UPS), all of which require true deep-cycle useability. A deep-cycle lead-acid battery is designed with thicker plates to withstand a greater depth of discharge (again, there’s nothing magical about the voltage, just the construction). But in the same way, people have started equivocating 6V batteries with all deep-cycle batteries. It’s a Venn diagram gone wrong!

You can use either 6V or 12V deep-cycle batteries. If they have the same type and quality of construction, they should give you equivalent life and performance. 

Pet Peeve: Don’t Believe Everything You Hear

I don’t usually take potshots at other websites, even ones I suspect are simply rewriting someone else’s content, but some of these claims are too egregious to ignore! Here’s a common false claim repeated by TheCampingAdvisor that you can get more amp-hours using two 6V batteries:

“You can get more amp hours by using 2 6-volt batteries. If the 12-volt option only provides 100ah and you connect a second battery, then you only get 200ah. Two 6-volt batteries connected correctly provide you with 225ah. Many RVers like that extra amp hour rating.”

This claim is misleading. Yes, many 12V batteries are 100 amp-hours, and many 6V batteries are 235 amp-hours, but you can find batteries of both voltages in several sizes. You don’t get an extra 225 Ah out of thin air!

The Real Reason 6-Volt Golf Cart Batteries Are More Popular

So if either battery works, why have 6V golf-cart batteries gotten so popular?

1. Cost and accessibility. 6V golf cart batteries are relatively cheap and easy to find (thank you, Costco). 
2. Weight and portability. An average golf cart battery weighs 40-70 lbs. It’s easier to move two smaller batteries than hoist a single giant battery!
3. Space constraints. Your coach or camper may have limited space for individual batteries. It may be easier to simply add on a second Group 24 battery rather than upsize to a Group 31 and retrofit.

Hot hint: The most recommended golf cart battery for upgrading your RV’s battery bank is a GC-2 deep-cycle battery.

Let the Flame Wars Begin! Series V. Parallel 

Now, this question of 6V vs 12V batteries can evoke some powerful emotional responses!

Proponents of 6V batteries in series will argue that if one battery dies, you only have to replace the “bad” battery, and you can cross your fingers you didn’t damage the “good” battery. Saves money in the long run.

Their opponents will point out that if a 6V battery dies, you’re dead in the water. You don’t have 12V system voltage anymore. But if you connect two 12V batteries in parallel (like an intelligent person) then you’re guaranteed power even if one battery dies, they say.

But then the 6V crowd comes back swinging and says that wiring batteries in parallel will shorten battery life because the cells won’t be balanced. When one battery starts to go, it’ll take down the other one with it. Plus, a lot of 12V “deep-cycle” batteries aren’t really even deep-cycle! 

“Nonsense!” retort the 12V fans. You can use a battery balancer to equalize cell voltage. And don’t you know major manufacturers like BattleBorn are focusing on 12V lithium deep-cycle batteries, not 6V? Do you enjoy being behind the curve?

“You Neanderthals!” scream the 6V crowd. Using a battery balancer AND 6V batteries in series minimizes the number of cells and wire connections, which reduces the chance of a shorted cell or loose terminal connection. Plus golf cart batteries are famous for their long life. They’re proven and trusted technology. 

“You Luddites!” curse the 12V crowd. Haven’t you ever considered that paralleled 12V systems can be expanded one battery at a time, but 6V battery systems turn into a spiderweb of series/parallel connections, and you have to buy two 6V batteries at a time? Did ya? DID YA?!

Ah well, you get the point. To each their own. Pros and cons. Some of us – myself included – enjoy debating the finer points of battery chemistry, but in this situation, both solutions work! Your RV is designed to operate on 12V power. Whether it comes from two 6V batteries wired in series, a single 12V battery, or a bank of 12V batteries wired in parallel makes very little practical difference. Half a dozen of one; six of the other.