How Do I Wire The Batteries On My RV Trailer

How Do I Wire The Batteries On My RV Trailer.

Why Connect More Than One Battery To An RV Trailer?

Why Connect More Than One Battery To An RV Trailer? A battery bank is a group of two or more batteries connected in series or parallel.

This allows you to store more energy than is possible with a single battery and increase amperage, voltage, or both. There’s always been a bit of confusion on this topic, so today we’re going to try and explain what you need to know about camper battery sequential cables.

Why Connect More Than One Battery To An RV Trailer?

Without an electrical connection, motor homes use more electricity than you might think. Every time you turn on the light, use the water pump, blower, or the oven is out of battery. Even when switching to liquefied gas (propane), the refrigerator consumes electricity.

No matter what type of RV battery or battery you’re using, it’s not a good idea to completely discharge it. Lead-acid batteries can only be discharged to about 50% before breaking down, lithium-ion batteries to about 20%.

Even if you have a generator or solar panels to charge your RV every day, you want a lot of stored energy so you can use as much power as you need day and night without damaging the RV’s battery.

One of the easiest ways to add more batteries to your RV is to add more RV batteries.

In this article, I will show you the best way to connect 12 volt and 6 volt batteries to your RV. I’m more focused on adding 12 volts of electricity to your RV than building a solar power bank.

Remember, I’m not a professional and my knowledge is very limited when it comes to large solar banks that require a lot of batteries.

How To install a battery in my RV Trailer

  1. Turn off all power draw, including lights and accessories. If the negative cable sparks during removal, a draw is still present.
  2. Notice the position of the battery in the tray in relation to polarity.
  3. Disconnect the cables, negative first, and remove the old battery.
  4. Make sure the carrier and the hold-down hardware are free of corrosion. 
  5. If not a maintenance free battery, make sure the new battery is filled with the proper amount of electrolyte. To top up the electrolyte, simply add distilled water until the correct volume is reached. You should never have to add acid to a battery because under normal circumstances, the acid level remains the same while the water level drops during the electrolysis process.
  6. Clean the terminal posts with a wire brush until the metal shines.
  7. Install new battery in the tray with same positions for polarity as noted in step 2.
  8. Connect cables to new battery.
  9. Install hold-down hardware.
  10. Test RV lights.

General Battery Charging Cautions

  • Be sure the area around the battery is well ventilated while the battery is being charged.
  • Ensure that the battery terminal connections are secure and not corroded.
  • Locate the charger as far away from the battery as the DC cables permit.
  • Never mount the charger directly above the batteries being charged. Gases from the batteries will corrode and damage the charger. It is also possible that the gases from the battery may cause an explosion or fire.
  • Never try to charge a frozen battery. Charging the battery when its temperature is lower than 0 degrees Celsius is inefficient and ineffective. If possible, warm the battery to room temperature before charging.

Differences in Charging Batteries

There is not much difference to charging batteries in series or parallel and then charging one battery. The basic idea is the same.
With a battery, you can connect the positive output of the charger to the positive terminal of the battery. Then connect the negative output of the charger to the negative terminal of the battery.

As long as you connect the battery properly, the idea remains the same. In the case of a battery, the positive load wire RV is connected to the positive terminal of the battery and the negative load wire to the negative terminal.

Regardless of whether you are charging a series of two 6V batteries or charging two 12V (or more) batteries in parallel, connect the positive output of the charger to the positive terminal connected to the positive RV charging cable. You can also connect the negative output of the charger to the negative terminal connected to the negative RV load cable. This helps ensure that the battery in the bank is evenly charged.

Make sure your charger has the same voltage as the bank you are charging it with. The 12V charger can charge any number of 12V or 12V parallel banks. However, if you have a special case of connecting in series with a voltage of 24V, 48V, or otherwise, you’ll want to make sure your charger matches that voltage.

You can also charge individual batteries in the bank with a charger that matches that battery and charge them individually. For example, if you have four 12V batteries in series but only one 12V charger, you can connect and charge each one individually.

Another thing you want to make sure is that your charger is classified according to the chemistry of the battery you are charging. Most deep cycle batteries have a similar charging profile, but lithium batteries require a slightly different voltage.

How To Correctly Wire Multiple 12 Volt Batteries To An RV Trailer

Connecting multiple 12V RV batteries to an RV is not that difficult and most people can do it themselves. But there are several ways to get the error which I’ll take a look at.

The goal is to properly parallel the 12 V battery so that the performance between all the batteries is balanced. This will allow all your RV batteries to last longer and perform better.

What do you need to Wire a battery to a RV Trailer?

The first thing you will need to connect the RV battery is the correct cable. The best size to use is 6-4 AWG copper wire, I recommend 4 AWG because the lower the resistance, the more efficient the battery-to-battery energy transfer.

As each setting differs slightly based on the size of the battery used and the storage space it contains, I recommend that you use a long red and black 4 AWG copper cable with the correct battery post connections.

The Windy Nation 4 AWG cable set (click to view on Amazon) is ideal for most deep cycle RV batteries and should have sufficient cable length for your intermediate connection.

If you plan to connect more than 4 RV batteries together or if you have some space between them, be sure to bring more cables just in case.

To do a good job, you’ll also need a crimping tool (click to view on Amazon). You can try without it, but your terminal connection might not be as strong or secure, which could cause more resistance or the battery won’t work at all.

What is parallel cable Wiring?

If you are connecting the batteries in parallel, join the positive pole with the positive pole and the negative pole with the negative pole. This will combine the batteries into one big one that still has the same voltage.

You cannot mix batteries of different voltages and it is not recommended to mix batteries of different ages and sizes, although you can do this in parallel.

I won’t go deep into the specifics of parallel connections as this article isn’t really about that.

The most important thing to know is that you are connecting 12V batteries in parallel. You want the voltage to stay the same, unlike connecting 6v batteries in series because you want to double the voltage.

Wrong way to connect 12 volt battery in parallel

This type of parallel connection 12V RV battery works technically. In the chart below you can see that the positive terminal is connected and the same is connected to the negative.


The faulty part is that the load cable connecting the battery to the RV is placed on the same battery.

This will put the greatest amount of stress on the first battery and the least amount of pressure on the battery will be the last in the queue. If you parallelize your RV’s batteries this way, the first battery will wear out faster than the other.

You want the load to be evenly distributed so that all the batteries are charged and discharged evenly.

The best way to connect multiple 12V batteries in parallel

I showed the worst way, now I will talk about the best but also the most difficult way to connect several 12V batteries in parallel.

In the graph below, you can see that all 12 volt batteries are connected to the external connection on the external battery. Each wire running on each battery must be the same length or you will add more resistance to one battery than the other and the circuit will become unbalanced.


The main disadvantage of this method is that not everyone has the space in their RV to add an external terminal post and the balance difference between this method and the others may not be enough to make it worthwhile.

When building a large solar bank with 8 or more batteries, you should use a method like this to keep all your batteries healthy, but for some extra RV batteries, you can connect in other ways to make the RV batteries balanced.

How to connect 2 12V batteries to the RV Trailer

Two 12 volt batteries connected in parallel is one of the most common arrangements and one provided by most RV dealers and manufacturers.

Even my caravan is equipped with two 12 volt deep cycle batteries in two plastic battery cases connected in parallel on the trailer drawbar.


In the graph above you can see that the terminals are connected in parallel with an even length of wire. The main difference between this cable and the one I got wrong is that the RV load cable is connected to a different battery.

This will distribute the load and with just two batteries you will have a symmetrical circuit.

How to connect 3 12V batteries to the motor housing
Once you add more than two batteries using the final battery charging wiring method, you become a little less efficient.

But adding another battery doesn’t make much difference, so I’d still suggest installing a 3-12 volt RV battery similar to the 2 battery method.


You will still need to attach the load cable to the end of the battery so that the average RV battery is pulled evenly. The media emits fewer amplifiers than the latter two, but the difference should be small enough not to be a big deal.

If you want three completely balanced RV batteries, you can use the best method I mentioned above or use the cross-diagonal method I talk about below.

How to connect 4 12V batteries to the RV Trailer

If you want to add 4 batteries to your RV, you need to enjoy some cables. You can still connect the terminals together like the battery 2 or 3 method, but things get very unbalanced.

The cross-diagonal method is an easy way to balance 4 or more batteries without having to use the terminal mount method shown in Figure 1.


It seems complicated, but if you follow each wire, you’ll find that it’s easier than it looks.

You can start by connecting two pairs of batteries with a short cable. Then take two pairs and connect them with a long cable. This unites the two groups. You connect your motor housing’s electrical wires to the central terminal, which has both short and long wires.

Make sure the negative and positive load wires are still connected to the two different batteries. If everything is connected correctly, the load cable will connect to the middle battery.

Both long and short wires are connected to each battery, which balances the resistance and keeps the 4 batteries level.

Adding several different connection types results in a better balance than using standard chain links with load wires at each end.

If you can’t place 4 batteries in a row in your home battery compartment, you can connect them diagonally to form blocks, as shown in the following graphic.


As you can see, each battery still has long and short connection wires and it still needs to be perfectly balanced.

Right now my trailer has 2 12V deep cycle RV batteries sitting on the tongue. When they finally stop charging, I plan to try to cite 4 RV batteries with long 12V AGM cycles as the best picks in this article for the best RV batteries.

After taking the measurements, I decided that I should be able to put everything on my tongue as shown in the chart below.


I can still use the cross-diagonal method to maintain battery balance, the only obstacle is finding a box that can hold all the batteries to protect them from the weather.

The reason I like to keep a charged battery at the front of the trailer is to maintain an evenly distributed weight for safer towing conditions.

How to properly connect multiple 6 volt batteries to the RV Trailer

A 6V RV battery can be a good choice if you want to increase the overall durability and boost of the battery. There are many pros and cons of 6 and 12 volt RV batteries, but it mostly depends on preference.

If you’re using a 6-volt RV battery, the wires will be slightly different. You have to increase the voltage to 12 volts, because no motor can run at 6 volts.

You can do this by connecting two 6 volt batteries in series and connecting the positive terminal to the negative terminal. By doing so, you increase the voltage, but not the current.

For example, if you have two 12V 100ah RV deep cycle batteries and you connect them in parallel, you will get 12 volts and 200 Ah.

If you connect two 200ah batteries with 6 volts in series, you get 12 volts, but the amplifier clock remains 200.

The good news is that you can combine series and parallel with a 6 volt battery so you can combine 4 or more and keep the voltage for your RV at 12 but increase the amp hours. I’ll take a look at each of the wiring methods below.

Note that you should not combine different 6 V amplifier batteries. They should be of the same size, type and age if possible.

How to connect 2 6V batteries to the motor housing
As previously mentioned, you must first connect a 6V battery in series to produce 12V. 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’ve graphed the wires in blue to make it easier to understand.


As you can see, you will be reconnecting the load wires that will power the RV with various batteries. You must not have both wires to charge a 6V battery.

How to connect 4 6V batteries to the motor housing
Once you have connected 2 6v batteries in series to make one 12v battery it is very easy to connect 2 more 6v batteries in series/parallel to increase the boost time.

You can do this by combining each pair of 6v batteries and then connecting them in parallel as if you were making 2 12v batteries.


Be sure to connect the load cable (RV power) to a different pair of 6V batteries as shown in the table above.

This helps to keep the battery in balance which in turn will last longer.

How to connect 6 6V battery to RV Trailer

You can make big batteries with 6V batteries, but using an RV, even if you have more than 4 6V batteries, will be very heavy.

However, if your power requirements are high, you can easily connect 6 6V RV batteries using the same serial/parallel method used above.


The batteries are fairly balanced, similar to connecting 3 12v batteries. You can use the cross-diagonal method to try and balance it out even more if you want, but the difference may not be enough to make it worth it.

How to connect 8 6V battery to RV Trailer

While the presence of 8 6V batteries in RVs is not very common, it may be a good choice for your method.


Frequently Asked Questions

Which AWG cable should I use to connect the RV Trailer battery?

4 AWG is best for connecting an RV battery, but you can use 6 AWG and get good results

Where can I connect the battery charger to multiple batteries connected to each other?

The battery charger must always be connected to the same battery terminal as the load cable.

This helps the battery charge at a constant rate so that neither battery gets charged while the others in the same circuit don’t charge enough.

Does your RV Trailer Need 2 Batteries?

If you want to use a 6-volt RV battery, you will need to have at least two to get 12-volt power.

If you plan to use a 12 volt battery only one is needed, but I recommend buying a large 100 V 12 V long cycle battery or two smaller RV 35-50ah long cycle batteries.

Can you mix batteries with different amps (ah)?

When connecting batteries in series, such as 6V batteries, you cannot mix different ah batteries.

With a parallel cable, such as a 12V battery, you can use different sizes of 12V batteries.

With this in mind, it is important not to mix batteries of different ages. I won’t be linking anything more than 6 months away.

How do you connect a 3 12 V battery to a RV Trailer?

It is very easy to connect 3 12V batteries in parallel to the motor housing. You can scroll up and see the chart labeled Figure 3 in this article for more information.

Should You Leave Your RV Trailer Plugged into The Power All The Time?

If you leave your RV on all the time, you need to check and make sure that your RV has a smart charger or 3 step in the converter.

Older RVs can only have one older charger in the converter, which can cause the battery to recharge, which can be just as dangerous for them as dying. If your motorhome has an older charger, you can easily replace it with another one.

If you have a smart charger or 3-step charger in your motorhome, you should always have the battery installed. Remember to maintain the battery regularly and check the water level if it is flooded with lead acid.

Should I connect the RV Trailer batteries in series or parallel?

The 12V RV battery should always be connected in parallel as you want to keep the voltage the same but increase the amplifier’s operating hours.

6V RV batteries must be connected in series in pairs to form a 12V battery. Once the two 6V batteries are connected in series, you can connect them to another pair of 6V batteries in parallel.

What is the difference between an RV battery in series and an RV battery in parallel?

When you connect batteries in series, you increase the voltage they turn off. For example, two 12v batteries in series make one large 24v battery which is too big to use in an RV.

So instead you put them in parallel because you only want to increase the amp clock, not the voltage.

Due to the increased voltage across the battery series connection, you can connect two 6V batteries to make an RV compatible 12V battery.

Do RV batteries in parallel last longer?

When properly connected and balanced, a 12 V battery connected in parallel can last a long time.

If they are not properly connected, the batteries connected directly to the motor housing can wear out faster than others.

It may be a little more difficult to connect batteries in series, but 6V batteries are known to be tough and the difference between 2 6V batteries in series versus 2 high quality 12V long cycle batteries in parallel is very small.

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