Wiring 6 & 12 Volt RV Batteries Properly
If you are going to buy new 12 Volt or 6 Volt batteries for your RV, it is important to know how to wire them properly so that you do not damage your RVs electrical system. Although this is an easy concept to understand, many people tend to get this wrong. Basically, there are two ways to wire your batteries: in series or in parallel. In RVs where 6 Volt batteries are used, you may need to use a combination of both these methods to get 12 Volt output and increase the amount of total Amp Hours simultaneously. Let’s discuss this further and provide some examples:
Batteries wired in series:

With batteries wired in series, the Voltage increases but the Amperage remains the same.
 Example: If you take two 6 Volt batteries that have a capacity rating of 220 Amp Hours each and you wire them in series, you will get a total of 12 Volts of power; however, the total Amp Hours will remain the same at a total of 220 Amp Hours.

With batteries wired in series, the positive (+) from one battery is connected to the negative () terminal of the other. The remaining free positive (+) terminal and negative () terminal are used to connect to your RV.

This is how you create 12 Volts from two 6 Volt batteries.
Following is a graphic that represents two 6 Volt batteries wired in series.
Take a look at the diagram above. Here we have two 6 Volt batteries wired in series. With the positive from one battery connected to the negative of the other battery you have in essence created one 12 Volt battery out of two 6 Volt batteries. As I stated before, when you wire batteries in series, the Voltage increases and the Amperage stays the same. That is why in this scenario we have 12 Volts output; however, even though each battery is rated at 220 Amp Hours, we are still only receiving a total of 220 Amp Hours. The only thing that has increased here is the Voltage. If in this scenario each battery was a 12 Volt battery, you would have a total of 24 Volts output (which would not be good for your RV).
Batteries wired in parallel:

With batteries wired in parallel, the Voltage remains the same but the amperage increases.
 Example: If you take two 12 Volt batteries that have a capacity of 210 Amp Hours each and you wire them in parallel, the Voltage will remain the same at 12 Volts; however, the total Amp Hours will increase to 420 Amp Hours.

With batteries wired in parallel, the positive terminal connects to the positive terminal of the next battery and the negative terminal connects to the negative terminal of the next battery.

This is how you increase the total amount of Amp Hours you can get out of your battery bank.
Following is a graphic that represents two 12 Volt batteries wired in parallel.
In this scenario we have wired two 12 Volt batteries in parallel. As a result, the Voltage has remained the same (at 12 Volts) however the total Amp Hours increases to 420 Amp Hours, which is the total of the two batteries added together.
In my 5th wheel, I used a combination of series and parallel wiring. By taking six – 6 Volt batteries and wiring pairs of batteries in series, I can basically create three 12 Volt batteries that I can then wire in parallel to increase the amount of total Amp Hours that are available. Let’s take a look at how this works:
Take a look at the diagram above. Since this scenario gets confusing for some people I am going to try to make it as simple as possible. This diagram consists of two 6 Volt batteries wired in series. If you were to take a digital Voltmeter and measure the Voltage from the combination of these two batteries (holding one probe at the free positive (+) terminal and one at the free negative () terminal) you would get a reading of 12 Volts. For all intents and purposes, you can now think of this as one 12 Volt battery. In this scenario the Voltage has increased but the amperage has remained the same.
Now if I want to ensure that I have more total Amp Hours for all my toys, all I have to do is take several of these 6 Volt battery combinations (that are wired in series to give me 12 Volts) and wire them in parallel. Take a look at the diagram below.
In this scenario we have taken six – 6 Volt batteries and wired them in series and parallel to give us 12 Volts and 660 Amp Hours of battery capacity. How did we end up with 660 Amp hours? Remember that each 6 Volt pair of batteries wired in series gives us 220 Amp hours. We have now wired the three pairs of batteries in parallel and when batteries are wired in parallel, the amperage increases. So since each pair produces 220 Amp Hours x 3 pairs = 660 Amp Hours total.