How To Wire Multiple 12V Or 6V Batteries To An RV

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 battery power to your RV is to add more batteries.

See Also: Best Deep Cycle RV Batteries (AGM, SLA, 12V, 6V) 2020

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.

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.

See Also: How Long Will An RV Battery Run The Furnace? + Calculations

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 you parallel wire 12V batteries. You want the voltage to same the same and you wire 6V batteries in series because you want them to output 12V.

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.

Having both of the load wires from the RV on the same battery will create an unbalanced circuit.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 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 batteries in parallel.

In the graphic below you see all the 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.

Using even lengths of wire to connect all the batteries creates the most balanced set-up.

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 batteries.

How To Wire 2 12V Batteries To An RV

Two 12 volt RV batteries 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.

Best way to wire 2 12V RV batteries.

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. This is the best way to wire two RV batteries and it cannot be improved upon.

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.

Acceptable way to parallell wire 3 12V RV batteries.

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.

The correct way to wire 4 12V RV batteries so they are balanced.

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.

See Also: Best Portable Solar Panel Charger For RV Camper/Boondocking

Each battery has both a long and short wire connected to it which helps balance out the resistances and keeps the 4 batteries even. Just 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.

Cross-Diagonal wiring on 4 12V RV batteries.

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.

How to fit 4 12V batteries on the tongue of a travel trailer.

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.

See Also: Review Of The Jackery Explorer 500 Portable Power Station

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.

How to wire 2 6V batteries to an RV.

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.

You can combine groups of 6V batteries using series/parallel to increase the amp hours for RV use.

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.

You can use the simple parallel method to wire 6 6V batteries together or even use the Cross-Diagonal Method.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.

See Also: Best Deep Cycle Battery Charger (Marine, RV, AGM)

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 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.

You can read more about it above in this article.

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.

by Jenni
Jenni grew up in a small town in Idaho. With a family that loves camping, she has been towing trailers since a very young age.

17 thoughts on “How To Wire Multiple 12V Or 6V Batteries To An RV”

  1. Great article. But I still have a question.

    I’ve got Six, 6 volts, series, then parallel. They are brand new, but two are slightly lower in voltage than the other four. I know it’s a warranty issue, but I bought them while travelling and taking them back is not an option.

    So, moving forward, is it best to put the two “lower volt” batteries on the outside of the wiring chain?

    I have them as you shown in your article, were in my case the two that are connected to RV load in are “First in line”

    My after thought is to have them in the middle set wired in series together as they might be causing more resistance the way I have it now.

    I value your knowledge. Thank you. Gary

    Reply
    • The problem with combining batteries that are different voltages in a battery bank, especially one with 6 batteries, is it can create an unsafe circuit. The larger batteries are going to try and charge the lower voltage ones no matter where they are placed in the circuit, which will result in overcharging and reduce the lifespan of all of the batteries. In a worse case scenario, it could even destroy the smaller voltage batteries.

      In large battery banks like yours, it’s even recommended to always use the same brand of batteries as different brands can have slightly different voltages even if the label says they are the same.

      Since all the batteries are new I would sell the two odd 6V batteries and buy two new ones that match the other 4 perfectly. Even though you may lose a little money initially your battery bank will be much safer and all the batteries will last longer which saves you money in the long run.

      Reply
  2. Hello Jenni,
    Thank you for your “balanced” 8 6v battery wiring design! Last night I compared all the configurations I could find on the web and agree that your scheme is the most balanced with the fewest resistance creating cables and terminals. I have jumped into the deep end on my RV battery problems as we are moving to more dry camping and less dependency on shoreline power occasions. I have questions that you might help me with and am hoping I’m not in over my head…

    I bought 8 6v 225Ah AGMs that I will wire in series-parallel identical to your last figure above. Understanding that all cables and connectors need to be the best quality copper I can find and all of identical length and resistance throughout. I perceive that less is more in terms of gauge? I’ll assume that 2 AWG is overkill and 6 AWG or smaller is just OK or climbing in resistance. Thank you for that recommendation!

    On the RV’s Converter/Charger:
    But what am I getting into going from 2 “weak” 90Ah (<180Ah total) 12v batteries as the RV with built with when going to 900Ah total in the bank? I will check the converter/charger to make sure it is a “smart charger” type but will I need to modify the converter/charger to accommodate a battery bank 5 times normal capacity? Is there a formula to determine what output my converter/charger should produce to service 900Ah of battery?

    On my solar panel charging:
    I have been using a 100W solar panel with a 30A charge controller which seemed to do just fine servicing the 2 “weak’ 12V batteries. Will an addition of one more 100W solar panel be sufficient to support a 900Ah bank?

    I’m treading in deep water here in terms of understanding… Help!

    Thanks again for great info!

    KC

    Reply
    • You will need to get a different kind of charger that will be capable of handling that amount of amp hours. This Go Power! GPC-100amp 4 stage converter charger (click to view on Amazon) can handle up to 10 batteries and should be able to handle 900Ah. I suggest putting the charger as close to the bank as possible and making sure the wiring is the right size.

      That being said I am not a professional and I can only help you with what I know. With a battery bank of that size in an RV I would suggest getting a professional to help you with the charging and wiring aspects. If it’s done right the batteries will last a long time but charging them wrong could ruin them.

      As for the solar panels. If you do the math two 100W solar panels will give you about 60Ah per day. At that rate, it would take 15 days to generate 900Ah. Of course, you probably won’t be using that much power daily but you will probably end up wanting more solar panels so you can recharge your power bank quicker.

      Reply
      • Jenni,
        I have upped my game a bit on the solar panels to service the 900Ah battery bank. Thanks for your help!
        In regards to your drawing above, which I intend to use, I have a question with respect to balancing all cables to equalize the resistance so no One battery gets charged any more or less than the others. So does that mean that if the cables that I use to “Bridge” the 2 banks of 4 is 20”, does that mean that the cables that tie them in parallel and the cables that connect in series (blue) all have to be 20”?

        Reply
  3. Jenni,

    My setup will be the same as “Travel Trailer Tongue” but in a metal, ventilated box behind the steps on my RV.
    Would it be advantageous to just flip the second and fourth battery in that diagram so that each cable will be the exact same length when you connect them together in a crosshatch pattern with three “X”s ? If so where would I connect the load cables?

    Dave

    Reply
    • Hey David,

      The cross diagonal method shown on the travel trailer tongue is about the same thing, you just don’t have to run the wires across the tops of the batteries. I think it will work about the same either way. Here’s a diagram with the 2nd and 4th batteries flipped to help show where the load cables should be connected.

      How to wire 4 12V batteries together with the 2nd and 4th batteries flipped.

      Reply
  4. Hi Jenni and thank you for such great information. I have two questions if you can please:

    We are going for off-grid stays in our van and I will be augmenting the existing 600a of lithium batteries with two additional batteries. They have one season with very few cycles and I have read that in parallel, mixing these with two new is not a concern. Is this ok?

    Also, assuming I wire two banks as you have shown for 400a, how should they connect and where should I take 12V power from?

    Much appreciated

    Reply
    • Hi John,

      As batteries are used and age they slowly lose their capacity. When you add a new one to the mix you are basically putting batteries with two different capacities together which is not recommended because either the newer battery will not get charged enough or the older battery will get charged too much which may damage it.

      However, if the lithium batteries in your bank have only been used a few times and you have kept them charged with a proper lithium battery charger they probably haven’t lost very much of their original capacity. There will be some difference between the new and old but probably not enough to damage the old batteries when charging. The thing that will most likely happen is the new batteries will lose some capacity a little quicker than they normally would.

      I agree that it’s probably not a big concern to add the two new ones.

      For your other question about the wiring, are you asking about parallel wiring 4 12V batteries together or 4 6 volt?

      Reply
      • Thank you for the response – and I agree. I am trying to fine a diagram for wiring 8-12V batteries in parallel.
        Thank you

        Reply
  5. Great article – thanks!
    I’m in the process of buying a 1999 National Dolphin. For the first 18 months it will be my weekend home on a lot I’ve recently purchased (while my house is being built). Let’s assume that the two 6 volt batteries currently installed are old. In my “perfect world”, I’ve got a 100W solar array that is charging two or four deep cycle batteries that keep me comfortable while I’m there, and then are kept charged during the week by the solar (I have a full south exposure). My questions:
    1. do I disconnect the two 6V for now, and just connect the cables to those leads?
    2. If I permanently wanted to move over two my new battery array, besides building a stable holder for them, do I need to do anything beyond ensuring that I connect the cables from my new batteries into the existing system? I expect I will be boondocking as I will do some cross country travel during the summer, so the strong battery backup will be of value.
    3. Is there any reason to consider doing this with 6V batteries v. 12V?
    4. can I have the solar charger connected to the battery array while I’m using the RV?

    Thanks in advance for any insights or redirects.

    SJ

    Reply
    • Hi SJ,

      1. Yes, I assume the old 6V batteries are wired in series, if you end up getting 12V batteries you will need to wire them in parallel. Also, never combine old batteries with new ones.
      2. No, but again you need to make sure you wire them right. If you go with lithium you will need to make sure you have a lithium compatible charge controller on your RV and solar panel. You can read more about charging lithium batteries in this article here.
      3. This is a good question that has a lot to do with personal preference. I have written an article about it you can find here.
      4. Yes.

      Hope this was helpful, good luck with the RV, if you have any more questions feel free to ask.

      Reply
  6. I want to connect two 12V batteries in series and parallel. Is this possible. This is on my boat so that I can charge the batteries with the 12V charging system from the boat motor and still be able to run my 24V trolling motor.

    Reply
    • Hey Marshall,

      Connecting your batteries in series for the motor and parallel for the charger won’t work. What you can do is connect a 12V charger to each battery (use 2 12V chargers) or get a 24V battery charger.

      Reply

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