How does a battery isolator work?

Updated March 23, 2017

A battery isolator is a one-way electrical battery that allows an electrical current to flow in one direction but not the other. A battery isolator typically is used in situations where multiple batteries are required, and its primary purpose is to ensure that the failure of a single battery will not incapacitate an entire electrical system. Battery isolators are used in large trucks, aeroplanes, boats, utility vehicles and other vehicles that require multiple batteries and backup sources of power.


A battery isolator separates multiple batteries from one another to ensure that a vehicle has access to a backup power source. In addition, a battery isolator ensures that a vehicle's electrical system does not pull power from multiple batteries at the same time, which would rapidly drain all the batteries and cause the electrical system to fail. A simple set-up is one in which a vehicle contains two batteries, both of which are attached to the isolator. The battery isolator is attached to the vehicle's alternator, which is the device responsible for providing the vehicle with electrical power and for charging the vehicle's battery. The battery isolator uses sensors to determine the number of batteries it is connected to and to draw power from the strongest battery. The idle batteries are charged by the alternator, and the battery isolator can switch power sources if the battery in use suddenly fails.

Diode Versus Solenoid Battery Isolators

There are two main types of battery isolators: the diode isolator and the solenoid isolator. A diode isolator uses two high-current diodes to direct the flow of current from the battery to the battery isolator. A diode isolator is not as complex as a solenoid isolator, is easier to maintain and repair and generally lasts longer.

A solenoid isolator uses several electrical relays to control the flow of electrical current. One of the relays receives the electrical current from the battery, while the other relay (known as the central relay) monitors the power levels of the idle batteries. Additional relays transmit the charging current from the alternator to the idle batteries. A solenoid battery isolator does not have as much current degradation as a diode isolator and is more efficient.

Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author