A battery isolator is a device that typically runs between a starter battery and a secondary battery. It can disconnect a battery from a power system either for charging or discharging purposes. Most often, however, these devices protect a secondary or backup battery from any unnecessary drain. For example,. To put it simply, these devices give users more control over their power systems. They're needed in muti-battery systems where the batteries need to discharge or charge at different times. Depending on your system's specific. Battery isolators are used in any situation that involves multiple battery banks in the same electrical system. For example, you can use them in vans, RVs, or boats to isolate the house batteries. Battery isolators are rated by the amperagethey can handle. Thus, you'll need to get a large enough battery isolator for your electrical loads. Many times, this is based on the amperage output of your alternator or generator. The type of battery isolator you need depends on your electrical system and the reason why you need one. Here are a few of the most common types.