Batteries Parallel Wiring

This is my third post in a series about RV electrical set-ups. Although the information is fairly basic it will help if you read the entire series.
Post #1 Deep cycle batteries
Post #2 Ratings and sizes

Batteries Parallel Wiring

There are two ways that batteries are typically wired, when there are multiple batteries being used for electrical power in your RV, that is either parallel or in a series. Parallel wiring is the most common. In this post I will describe parallel wiring. Parallel wiring does not increase the voltage, so when two 12 volt batteries are wired in this way it remains a 12 volt system. here is an example:

2 battery parallel wiring


the effects can be seen when jump starting a car. The battery in the dead car remains 12-volts, and will still turn the starter, but only very slowly. Parallel wire a charged up 12-volt battery to the weak battery, and the dead car turns the starter at the required speed and the car starts immediately. Parallel wiring the charged battery to the weak battery did not alter the voltage – it remained a 12-volt system. The car’s system is 12-volt, and running greater voltages through that system would be destructive to it. To avoid increasing the voltage and damaging the vehicle, the batteries are simply parallel wired.


Two 12 volt batteries wired in parallel means that the positive post of each battery is connected to each other, and the negative posts are also connected together. Connecting the lead of the positive side of one battery to the load, and the lead of the other battery’s negative side to the load is the best practice. In parallel the voltage remains the same, but the amount of current available increases. Batteries connected in parallel should be the same brand, type, size, and age. Otherwise long-term capacity could be reduced. It is possible to connect more than two batteries together in parallel, but space is a major hindrance in a RV setting.

It is recommended that if you are going to wire more than two batteries together in a parallel system that they share a common positive connection, and a common negative connection. This will best allow each battery to be charged correctly. Again using the same brand, type, size, and age are important factors for the life of the batteries.

How many batteries do you use in your set-up (motor home, or travel trailer)? How long are you off the grid usually?

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