Why Connect More Than One Battery To An RV?
When not connected to power an RV uses more electricity than you think. Every time you turn on a light, use the water pump, a fan, or the furnace power is being drained from the batteries. Even when switched over to LP gas (propane) the fridge is using electricity.
No matter what kind of RV battery or batteries you are using it’s not good to drain them all the way. Lead-acid batteries can only be drained down to around 50% before taking damage and Lithium-ion around 20%.
Even if you have a generator or solar panel to charge the RV batteries every day you are going to want a lot of stored power so you can use as much electricity as you need each day and night without damaging the RV batteries.
One of the easiest ways to add more battery power to your camper is to add more RV batteries.
In this article, I’m going to show the best ways to wire both 12 volt and 6 volt batteries to your RV. I’m focusing more on adding 12 volt power to your RV not creating a solar power bank.
Note that I’m not a professional and my knowledge is very limited when it comes to large solar power banks that require a lot of batteries.
How To Correctly Wire Multiple 12 Volt Batteries To An RV
Wiring multiple 12V RV batteries to an RV isn’t very difficult and most people can do it themselves. But there are a few ways to do it wrong that I’ll go over.
The goal is to wire the 12V batteries together in parallel the right way so the power is balanced between all the batteries. This will make all your RV batteries last longer and work better.
What You Will Need
The first thing you need to wire RV batteries together is the proper wire. The best sizes to use are 6-4 AWG copper wire. I suggest 4 AWG because the less resistance the more efficient the transfer of power is from battery to battery.
Because every set-up is going to be a little different depending on the sizes of batteries used and the storage area they go in I suggest getting a long length of red and black 4 AWG copper wire with the right kind of battery terminal connectors.
The Windy Nation 4 AWG Wire Kit (click to view on Amazon) is perfect for most deep cycle RV batteries and there should be enough wire length for your average connections.
If you plan on wiring together more than 4 RV batteries or they will have some distance between them you may want to get more wire just in case.
To do the job right you will also need a crimping tool (click to view on Amazon). You can try without it but your terminal connections might not be as tight or secure which could mean more resistance or a battery that isn’t working at all.
What Is Parallel Wiring?
When you connect batteries through parallel you are combining the positive terminals to the positive ones and the negative to negative. This combines the batteries to create one large one that still has the same voltage.
You cannot combine batteries of different voltages and it’s not recommended to combine different ages and sizes of batteries even though it is possible to do so through parallel.
I’m not going too deep into the specifics of what a parallel circuit is because that’s not really what this article is about. You can read more about parallel and series wiring here if you want to learn more.
The main thing you need to know is that you parallel wire 12V batteries. You want the voltage to stay the same unlike when you wire 6V batteries in series because you want to double the voltage.
The Wrong Way To Parallel Connect 12 Volt Batteries
This way of parallel connecting 12V RV batteries does technically work. You can see in the graphic below that the positive terminals are connected and the same with the negatives.
The wrong part is the load wires that connect the batteries to the RV are both placed on the same battery.
This puts most of the pressure on the first battery and the least amount of pressure on the battery last in line. If you parallel wire your RV batteries like this the first batteries are going to wear out much faster than the other ones.
You want the load to be evenly distributed so all the batteries are charging and discharging the same.
The Best Way To Parallel Wire Multiple 12V Batteries
I’ve shown you the worst way, now I’ll talk about the best way but also the most difficult way to wire multiple 12V batteries in parallel.
In the graphic below you see all the 12 volt batteries are wired to external battery terminal posts. Each wire running from each battery needs to be the same length otherwise you will be adding more resistance to one battery than others and the circuit will be unbalanced.
The main downside to this method is not everyone has space in their RV to add external terminal posts and the difference in balance between this method and others may not be enough to make it worth it.
If you are creating a large solar power bank with 8 or more batteries you are going to need to apply methods like these to keep all your batteries healthy but for a few extra RV batteries, you can wire in other ways to create balanced camper batteries.
How To Wire 2 12V Batteries To An RV
Two 12 volt RV batteries wired in parallel is one of the most common set-ups and the one most RV dealers and manufacturers make room for.
Even my travel trailer came with two deep cycle 12 volt batteries in two plastic battery boxes wired in parallel on the tongue of the trailer.
In the graphic above you see that the terminals are wired in parallel using even lengths of cable. The main difference between this wiring and the one I called wrong is the load wires from the RV are connected to different batteries.
Doing this distributes the load and with just two batteries you will have a balanced circuit.
How To Wire 3 12V Batteries To An RV
Once you start adding more than two batteries using the method of wiring the load wires on the end batteries start to get a little less efficient.
But just adding one more battery isn’t going to make a huge difference, so I still suggest wiring a 3 12 volt RV battery set-up in a similar way to the 2 battery method.
You still need to put the load wires on the end batteries so the middle RV battery is being drawn from evenly. The middle will be putting out fewer amps than the end two but the difference should be small enough that it’s not a huge deal.
If you want three absolutely perfectly balanced RV batteries you can use the best method I mentioned above or apply the Cross-Diagonal method I talk about next.
How To Wire 4 12V Batteries To An RV
If you’re going to add 4 batteries to your RV you are going to have to get a little fancier with the wiring. You can still just chain the terminals together like the 2 or 3 battery method but things will be very unbalanced.
The Cross-Diagonal method is a simple way to keep 4 or more batteries balanced without having to apply the terminal post method seen in Graphic 1.
It looks complicated but if you follow each wire you will start to see that it’s easier than it looks.
You can start by connecting two pairs of batteries using a short wire. Then take the two pairs and connect them using one long wire. This combines the two groups. You connect your load RV Power wires to the center terminal that has both the short and long wire on it.
Make sure the negative and positive load wires are still connected to two different batteries. If everything was wired right the load wires will connect to the middle batteries.
Each battery has both a long and short wire connected to it which helps balance out the resistances and keeps the 4 batteries even.
By adding a few more different kinds of connections, a better balance has been created than if you were to use the standard chain connections with the load wires on each end.
If you can’t fit 4 batteries in a row in your RV battery storage space you can connect them the Cross-Diagonal way in a block as shown in the graphic below.
As you can see, each battery still has a long and short connecting wire and should still be perfectly balanced.
Right now my travel trailer has 2 12V deep cycle RV batteries sitting on the tongue. When they finally stop holding a charge I plan to try and fit 4 12V AGM deep cycle RV batteries like the top choice in this article on the best RV batteries.
After measuring, I found that I should be able to fit them all on the tongue like in the graphic below.
I’ll still be able to use the Cross-Diagonal method to keep the batteries balanced, the only obstacle will be finding a box that can fit all the batteries to keep them protected from the weather.
The reason I want to keep the batteries loaded on the front of the travel trailer is to keep the weight evenly distributed for safer towing conditions.
How To Correctly Wire Multiple 6 Volt Batteries To An RV
6V RV Batteries can be a good choice if you are looking for an increase in durability and total amp hours in a battery. There are many pros and cons to both 6 and 12 volt batteries for RVing but it mostly comes down to preference.
You can read more about each kind of RV battery set-up and its pros and cons here.
If you’re going with 6 volt RV batteries the wiring is going to be a little different. You need to increase the voltage to 12 volts because no RV is made to run on 6 volt power.
You can do this by wiring two 6 volt batteries together in series by connecting a positive with a negative. When you do this you increase the voltage but not the amperage.
For example, if you have two 12V 100ah deep cycle RV batteries and you wire them together in parallel you end up with 12 volts and 200ah.
If you wire two 200ah 6 volt batteries together in series you end up with 12 volts but the amp hours remain 200.
The good news is you can combine series and parallel wiring with 6 volt batteries so you can combine 4 or more and keep the voltage at 12 for your RV but increase the amp hours. I’ll go through each of these wiring methods below.
Note that you should never combine different amp hour 6V batteries. They must be the same size, kind, and, if possible, age.
How To Wire 2 6V Batteries To An RV
As I mentioned before the first thing you need to do is connect the 6V batteries in series to create a 12V one. You do this with a small piece of wire preferably the 4 AWG copper wire I mentioned in the 12V section of this article.
The color doesn’t matter and I made the series wire blue in the graphics so they are easier to understand.
As you can see, you will still attach the load wires that will power the RV to different batteries. You should never have both load wires on one 6V battery.
How To Wire 4 6V Batteries To An RV
Once you’ve wired 2 6V batteries in series to make a 12V battery it’s really easy to wire 2 more 6V batteries together in series/parallel to increase the amp hours.
You can do this by combining each pair of 6V batteries and then wiring them together in parallel like you would 2 12V batteries.
Make sure you connect the load (RV power) wires to the different pairs of 6V batteries as shown in the graphic above.
This will help keep the batteries balanced which in turn keeps them lasting longer.
See Also: When To Charge A Deep Cycle Battery
How To Wire 6 6V Batteries To An RV
You can make huge battery banks using 6V batteries but for RV use even having more than 4 6V batteries is going to weigh a lot.
But if your energy needs are high you can easily wire 6 6V RV batteries together using the same series/parallel method used above.
The batteries will be reasonably balanced much like wiring 3 12V batteries together. You can use the Cross-Diagonal method to try and balance them even more if you want but the difference may not be enough to make it worth it.
How To Wire 8 6V Batteries To An RV
While having 8 6V batteries in an RV isn’t super common it may be the right choice for you so I thought I’d add this diagram to illustrate how 8 6V RV batteries can be wired in series but also balanced using the Cross-Diagonal method.
Frequently Asked Questions
What AWG of wire should be used to connect RV batteries?
4 AWG is going to be the best for connecting RV batteries but you can also use 6 AWG and get good results.
Where do I connect the battery charger on multiple batteries wired together?
The battery charger should always be connected to the same battery terminals the load wires are connected to.
This will help the batteries charge at an even rate so no battery is getting overcharged while another on the same circuit isn’t getting charged enough.
Does an RV need 2 batteries?
If you are going to use 6 volt RV batteries then you have to have at least two of them to reach 12 volts of power.
If you are going to use 12 volt batteries only one is necessary but I suggest getting either a large 100ah 12V deep cycle RV battery or two smaller 35-50ah 12V deep cycle RV batteries.
Can you mix batteries with different amp hours (ah)?
When connecting batteries in series as you would with 6V batteries you cannot mix different ah batteries.
When wiring in parallel like you would with 12V batteries you can use different sizes of 12V batteries.
That being said it’s important to try and not mix different ages of batteries. I wouldn’t wire anything together that is older than 6 months apart.
How do you hook up 3 12V batteries to an RV?
It’s easy to wire 3 12V batteries in parallel to an RV. You can scroll up and check out the diagram labeled graphic 3 in this article for more information.
Should you leave your RV plugged in all the time?
If you are going to leave your RV plugged in all the time you should check and make sure your RV has a smart or 3 stage charger in the converter.
Older RVs may only have an older kind of trickle charger in the converter which can cause your batteries to get overcharged which can be just as bad for them as going dead. If your RV has an older charger in it you can swap it out for a different one pretty easily.
If you do have a smart or 3 stage charger in your RV it should be safe to leave the batteries plugged in all the time. Remember to do regular maintenance on the batteries and check the water levels if they are flooded lead-acid.
Should I wire my RV batteries in series or parallel?
12V RV batteries should always be wired in parallel because you want to keep the voltage the same but increase the amp hours.
6V RV batteries need to be wired in series in pairs to create a 12V battery. Once two 6V batteries are wired together in series you can wire them to another pair of 6V batteries using parallel.
What is the difference between RV batteries in series and RV batteries in parallel?
When wiring batteries in series you are increasing the voltage they will put out. For example, two 12V batteries wired in series will become a large 24V battery, which is too large for RV use.
That’s why you wire them in parallel instead because you only want to increase the amp hours, not the voltage.
Because of the increased voltage when wiring batteries in series you can connect two 6V batteries to create a 12V battery that is compatible with an RV.
Do RV batteries in parallel last longer?
When wired the correct and balanced way 12V batteries wired in parallel can last a long time.
If they are wired incorrectly the battery the RV is directly connected to may wear out faster than the others.
It can be slightly harder on batteries to be wired in series but 6V batteries are known to be tough and the difference between 2 6V batteries wired in series compared to 2 high quaility12V RV deep cycle batteries wired in parallel will be very small.
Have any more questions about wiring multiple RV batteries? Leave a comment below.