The Value of a Battery Isolator on Your Boat

Battery isolators in marine applications have been used to maintain and direct the engine alternator DC charging in boats with multiple battery banks for decades. There are a number of reasons for installing an isolator in a boat with multiple batteries. First and foremost, the isolator can isolate the engine starting battery from the house/accessory battery or batteries. Second, the isolator will charge the battery bank with the lowest state of charge, then the next lowest bank, and so on when multiple battery banks are used. In twin engine applications where each engine has its own alternator, the isolator utilizes both alternators to the best of their ability and allows charging of all battery banks when just one engine is running. Keep in mind that the rate of charge is based on the alternator amperage output capacity.

Keeping Your Batteries Separate

Separating the starting battery from the house bank on a boat prevents the starting battery from being discharged when the engine is not running and DC accessories are being used. Devices like fish finders, stereos and lighting can discharge an engine battery and prevent the engine from starting to get home. Having separate battery banks - one for starting and one for accessories - in combination with an isolator will keep the starting battery from becoming discharged. Once the engine is started, the isolator will then direct DC alternator charging current back to the depleted accessory battery.

Making Batteries More Efficient

Another feature of an isolator is that it will recognize the battery bank with the lowest state of charge and direct the DC alternator output to that battery or battery bank. Then, once it is brought even in state of charge to the other battery it will direct charging equally to both banks.

A battery isolator will also allow one engine alternator, in a twin-engine boat, to charge both starting batteries along with the house battery bank when only one engine is running. In some instances, this can be an advantage if only one engine is used for trolling while fishing or there is an engine problem and only one engine will operate.

Using a Battery Isolator Effectively

A battery isolator works best when the alternator sensing is done at the battery. Some isolators have a sensing connection that can be wired to the alternator sensing terminal. The reason for this sensor is that the diodes in the isolator create some parasitic voltage loss. The battery charging will be more accurate when alternator sensing is at the battery or isolator sensor terminal. To choose the correct isolator for your application, you will need to know the size of the engine(s) alternator along with the number of battery banks being charged.

Managing Batteries Without Isolators

Battery charging to multiple batteries or battery banks can be controlled through manual switching instead of using battery isolators. It requires a knowledge and understanding of the boat’s battery layout and electrical demands. You also need to remember when to turn the switch On or Off! In addition, there is newer technology such as Automatic Charge Relays (ACRs) and Automatic Combiners that will accomplish battery charging similar to an isolator but we’ll save that for another article posting.

In today's world with all the options and accessories available on a boat, having and utilizing multiple batteries is common place. Having a battery isolator that is properly sized and correctly installed is an excellent upgrade. They're ability to separate and utilize alternator charging to the best of its ability provides confidence along with get home peace of mind.  For assistance identifying the right battery isolator or other electrical components for your vessel, please give the knowledgeable folks at Marine Parts Source a call at 866-388-0390.