A battery isolator is a one-way electrical valve, allowing DC current to flow in one irection, but not flow in reverse. They are commonly used on vehicles where multiple batteries or battery banks are used, including recreational vehicles, boats, utility vehicles, airplanes, and large trucks. The primary purpose for their use is to insure that a failure of a single battery or battery bank, will not wipe out an entire battery network. These are also used in vehicles with large car stereos which require multiple batteries.