What Is a Battery Isolator?


If you own a multi-battery system, you may be wondering about the best way to connect them. One of the main advantages of having multiple batteries is backup power. However, you need to prevent one battery from unintentionally draining the others. This is where a battery isolator comes into play. Let’s delve deeper into this topic.

What is a Battery Isolator?

A battery isolator is a device that is typically placed between a starter battery and a secondary battery. Its main function is to disconnect a battery from a power system to facilitate charging or discharging. However, in most cases, the primary purpose of these devices is to protect secondary or backup batteries from unnecessary drain.

How Does a Battery Isolator Work?

When the engine is running and the alternator is charging the starter battery, it also charges the secondary battery. However, when you turn off the engine, you don’t want the batteries to remain connected. In the case of different battery chemistries, such as lead acid starting and lithium house batteries, it’s also important not to connect them together. This is where the isolator comes in. When the engine is off, the isolator physically isolates the second battery, allowing it to retain its charge.

The Importance of Battery Isolators

Battery isolators are crucial for giving users more control over their power systems, especially in multi-battery setups where batteries need to discharge or charge at different times. They prevent unintended and uneven battery discharge and can be used to disconnect a backup battery when needed.

Where are Battery Isolators Used?

Battery isolators are commonly used in vehicles, RVs, boats, and other off-grid electrical systems that involve multiple battery banks. They are employed to isolate house batteries from the alternator and starter battery when the engine is not running. They are also used to prevent two lead-acid batteries from draining each other.

Choosing the Right Battery Isolator

The type of battery isolator you need depends on your electrical system and the specific requirements you have. Here are a few common types:

Manual Isolators

If you only need to isolate a secondary battery for backup electricity, a manual battery isolator could be sufficient. It typically consists of a switch that allows you to connect or disconnect the backup battery. However, keep in mind that these switches won’t prevent accidental battery drain if left on.

Relay-Based Isolators

If your goal is to protect the starting battery by isolating it from the secondary battery or the alternator, a relay-type battery isolator with external control is a better option. This type of isolator helps prevent power drain from both batteries and protects against a massive drain on both batteries.

DC-DC Charge Isolators

DC-DC charge isolators offer a more complex solution by including charge control. These units allow specific control of current flow between batteries, ensuring proper charging of the secondary battery. They are commonly used in engine battery systems to prevent overtaxing the alternator when charging lithium batteries.

Diode Battery Isolators

Diode battery isolators are useful for preventing multiple lead-acid batteries from draining each other. These isolators allow power to flow from an external power source to the batteries but not between the batteries themselves.

Rating Battery Isolators

Battery isolators are rated based on the amperage they can handle. It’s important to choose an isolator that can handle the maximum amperage output of your alternator or generator source to prevent overloading and potential damage.

Do You Need a Battery Isolator for Dual Batteries?

Having a battery isolator is not necessary for every multi-battery system. However, if your batteries serve different purposes or you have a backup battery, these devices are highly recommended. Battery isolators give you control over the flow of electrical current, protecting your batteries and ensuring reliable power in critical situations.


A battery isolator is an essential component for managing multi-battery systems. It allows you to control the flow of current and prevent unnecessary drain or damage to your batteries. Whether you’re on the road, at sea, or on an off-grid adventure, having a battery isolator ensures that you always have a reliable power source. If you have any questions about battery isolators, feel free to drop them in the comments below!

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