Battery Switches on a Boat

Our range of battery switches includes single and double-pole master battery isolators, along with changeover battery switches featuring alternator disconnect and key-lock options.

A Basic [ON/OFF] Switch

This is ideal for isolating a single bank of batteries when they are not in use to prevent voltage leakage and to prevent any risks of short circuits in the system.

Although this switch is easy to use, there are some common mistakes people make:

Leaving the switch on when the boat is not in use. Many electrical systems have small continuous loads, such as alarms or monitoring equipment, which can slowly drain the battery over time.
Installing the switch too far from the battery. If the switch is located too far away, a large section of cable remains live even when the switch is turned off. This increases the risk of short circuits or accidental damage to wiring.
Using a switch with an insufficient current rating. Not all battery switches are designed to handle the same electrical loads. Using a switch with a current rating that is too low can cause overheating, switch failure, or voltage drop.
Poor cable Connections. Loose or corroded battery cables connected to the switch can cause high resistance, voltage drop, and unreliable electrical performance. All connections should be clean, tight and protected from corrosion.

A Change Over Switch [1/2/ON/OFF]

This is used when the user has two battery banks, one for starting the engine and the other for domestic use. Being able to switch between the batteries means you can control where you would like the charge to go, either split equally to both battery banks, the engine start battery or the domestic battery.

Also when the engine is not running the user can choose which battery will be discharged. This is ideal to make sure you only discharge your domestic batteries ensuring you will always have enough charge in your engine batteries to be able to restart your engine.

This simple manual system has little to go wrong, however, they are required to be personally switched over so it is your responsibility to ensure the system is being managed correctly.

Position 1:

When the switch is set to 1, the boat’s electrical system is connected only to Battery 1. This battery is often used as the engine start battery, meaning all power for starting the engine and running electrical systems will come from this battery alone.

Position 2:

When the switch is set to 2, the electrical system is connected only to Battery 2. This battery is commonly used as the domestic battery, supplying power to onboard equipment such as lighting, pumps, navigation electronics, and other accessories.

ON/BOTH

The ON position (sometimes labelled BOTH or ALL) connects both batteries together. In this mode both batteries supply power to the electrical system. The alternator can charge both batteries simultaneously. This position is sometimes used when additional starting power is required, such as if the engine start battery is low.

OFF

When the switch is set to OFF, both batteries are completely disconnected from the boat’s electrical system. This position is typically used when the boat is not in use, maintenance is being carried out or the electrical system needs to be safely isolated.

Battery Split Chargers (Split Charge Diodes)

If you would prefer a less manual system, then these may be a better option for you. They are installed on the charge side, in-between the alternator and battery banks. They automatically sense which battery has the lowest voltage and put the most charge into that, until they reach an equal voltage then they split the charge equally.

This is a great simple system to ensure both battery banks are well maintained and also due to the nature of a diode (an electrical one way valve) they also prevent either battery discharging into the other.

However, like with most great things, there is a slight disadvantage and there is a slight voltage drop. The SIC units are very minimal compared to some others available with a voltage drop of only 0.2 Volts. Whilst the Victron Argo FET Isolators are less than 0.02 volts at low current and only around 0.1 volts at higher currents.