Batteries Series Wiring

This is my 4th post in a series about RV electrical set-ups. Although the information is is fairly basic it will help if you read the entire series.

Post #1 Deep cycle batteries

Post #2 Ratings and sizes

Post #3 Parallel wiring

In my previous post I talked about the most common way RV batteries are wired when there are multiple batteries being used for electrical power in your RV. In this post I will describe series wiring. To wire two batteries in a series you connect the negative lead to the positive lead of the second battery. The open posts of each battery are connected to the load. Keep in mind each battery increases the voltage. In the example below two 6 volt batteries connected in a series create a 12 volt output.

Likewise if two 12 volt batteries were wired together in a series you would have a 24 volt output. Most autos, motor-homes, and travel trailers operate with 12 volts.

So why would you use two 6 volt batteries wired in a series to run a 12 volt system? I’ve heard competing opinions on this topic. There is one school of thought that says 6 volt golf cart batteries have higher reserve capacity and are constructed better for deep cycle discharges than a 12 volt deep cycle battery. There is another school of thought that says today’s 12 volt deep cycle batteries are constructed just as well as golf cart batteries.

What set-up do you use?

Batteries Deep Cycle

I was talking with a friend about his RV set-up that allows him to go hunting and stay off the grid for weeks at a time. I thought this info might be helpful to RV’ers of all kinds so I’m going to do a series on batteries, which will lead into solar set-ups too. Just so you know I’ll be using references from the “RV Repair & Maintenance Manual” by Bob Livingston Trailer life books 1998.

The electrical system in your RV runs on two types of current; AC (alternating current) the same as your house, and DC (direct current) the same as your car. The stronger your DC system, the longer you can remain off the grid. The terms you need to understand are amps, watts, and volts. Most RV’s run on a 12 volt system, but did you know 2 – 6 volt batteries wired in a series will run your lights and appliances longer than 1 – 12 volt battery? Before you go and replace your batteries lets look at some basic information in this post, and the pros and cons along with the requirements of each set-up in posts to follow.

Batteries are not created equal

  • A car’s battery is designed to provide a very large amount of current for a short period of time. This surge of current is needed to turn the engine over during starting. Once the engine starts, the alternator provides all the power that the car needs, so a car battery may go through its entire life without ever being drained more than 20 percent of its total capacity.

  • A deep cycle battery is designed to provide a steady amount of current over a long period of time. A deep cycle battery is also designed to be deeply discharged over and over again, something that would ruin a car battery very quickly. To accomplish this, a deep cycle battery uses fewer, but thicker lead plates often coated with antimony or calcium, which increases the hardness of the plate.

Deep cycle batteries tend to cost more than the average car battery, but buying a regular car battery for your RV will only save you a few dollars on the short run. It will wear out quicker making it necessary to replace sooner.