Battery Selector Switches / Changeover Switches for Boats

A battery selector switch, aka battery changeover switch, is the safest way to connect two separate batteries and use them both or individually. To put it more simply, you choose which battery (or both depending on the model) to use as a starter battery, to recieve charging current and to run the loads on your boat. Why is this important? Let's say your starter battery is flat and your engine won't start. With a battery selector you can switch to the service batteries to start the motor. This is just one of the advantages battery selector switches have over battery isolators. In our online shop you can buy quality battery selector switches for 12V or 24V on-board electrical systems.

  Marine battery selector switches/battery changeover switches

- The easiest way to distribute charging current - 

What are battery changeover switches?

 - The battery switcher - boat energy management -

Battery changeover switches, also called battery selector switches, are primarily used, like all battery switches, for on-board safety and efficient energy management on your boat. They connect or disconnect the batteries from the on-board power supply. The switches prevent the batteries from discharging during times when the boat is not in use. Battery selector switches are slightly different to simple battery switches in the number of positions on the switch, which is greater. In addition to the basic on/off position on a battery switch, (aka battery main switch, kill switch or nato bone switch), a battery selector can also be used to switch between two batteries or use both together. Starter or service batteries can be specifically selected via a selector switch, usually via an easy-to-grip rotary knob. Both batteries can also be used at the same time, and the selector switch also acts as a battery master switch with which the entire electrical system on board can be shut down. A boat battery switch 1-2 or all battery selector switch is normally a three or four-position switch Off (off or 0), battery 1 (starter), battery 2 (service), or (Off, Bat 1, Bat 2, Both). 

Here is an overview of the main functions:

1. A battery selector distributes the charging current (of the alternator) to two batteries,

2. used to select the battery (energy source) from which electrical consumers (e.g. the starter motor) are to be supplied with power and

3. (depending on the version) also acts as a disconnector to reliably separate consumers and batteries from each other.

Unfortunately, an automatic battery switch will not be able to handle the aforementioned tasks. This is because the functionality and range of use is too complex.

Instead, individual components are used, such as voltage-sensitive charging relays (VSR) or other charging current distributors to distribute the current to the batteries or battery monitors that automatically disconnect the batteries from the consumers to protect them from deep discharge.

What are the advantages of battery changeover switches /selector switches for boats?

The advantages of battery selector switches compared to simple battery switches are that you can choose which battery is to be used or charged depending on the situation. For example, if your starter battery is depleted or faulty, you can switch to the service battery by simply turning the knob - or if both batteries are running low, you can combine the two and use to start the engine, for example, thus quickly avoiding an emergency situation from occurring. If your service battery is heavily depleted, you can select it to be charged via solar or wind energy, for example. Energy management optimisation is especially useful on longer voyages.

The switch is uninterruptible. This means that battery selection is also possible when the engine is running - however, this cannot be done via the off position! It should also be noted that when the switch is set to 'Service battery', the starter is also supplied via the service battery. If this is a gel battery, it is possible that it will not be able to provide a sufficiently high cold start current due to its higher internal resistance.

What electrical systems are battery selector switches designed for?

Boat battery selector switches are designed for use on all common 12 V or 24 V on-board electrical systems. In our online shop you will find various products from different manufacturers that are suitable for both outboards and inboards, i.e. built-in petrol and diesel engines. Continuous / short term peak power in a 12 V electrical system is up to 350 amps / 2000 amps, depending on the model. This makes them suitable not only for use on boats and yachts but also for caravans, mobile homes or trucks.

How do I install a battery changeover switch/selector switch?

The battery changeover switch should be installed as close as possible to the batteries. However, a common place is also on switch panels. Most of the switches can be flush or surface mounted. They have 3 connection bolts, one for battery 1, one for battery 2 and a common input or output to which charging sources and/or consumers are connected. However, certain devices, such as bilge pumps, alarm systems, or memory supply for important navigation instruments should be directly connected to the battery to prevent accidental disconnection. Batteries (or battery banks) should be connected to the changeover switch using a sufficient cable connection (see instructions for the respective product). Cables should be appropriately fused depending on their cross-section - by means of automatic circuit breakers or suitable strip fuses.

What is the danger when using battery selector switches?

When using battery selector switches, care must be taken to prevent both batteries being accidentally discharged due to the switch position set incorrectly ("both" (1 + 2)).  

What is the difference between a battery changeover switch and a marine battery isolator switch?

Some boats have two or more batteries that can be used on board either alternately or simultaneously. A battery selector switch is used to route load and charge currents to and from the batteries as selected, to connect batteries to each other or to disconnect both batteries from the vehicle electrical system at the same time. You could also do the same using two or three individual marine battery isolators, but it would take considerably more material and installation effort. Battery changeover switches have three connection points, one for battery 1, one for battery 2 and a common connection point from which it is possible to switch to battery 1 or to battery 2 or to both batteries (1 + 2). boat battery switch 1-2 or all


Fig. 3 Battery selector with switching function 1 / 2 / 1 + 2 / OFF

What do the manufacturer's specifications mean for battery switches?

The manufacturer's specifications are almost self-explanatory.

- Continuous load capacity with continuously flowing current.

- Short-term load capacity for a few minutes.

- Short-term load capacity for a few seconds, for example when starting the engine.

- Maximum permitted voltage.

The maximum permitted voltage is not the nominal voltage of the on-board power supply, but the actual maximum permitted voltage! According to DIN EN ISO 10133, the voltage measured at the battery terminals may be 75 % to 133 % of the nominal voltage. This is max. 16 V in the 12 V electrical system, max. 32 V in the 24 V electrical system, max. 48 V in the 36 V electrical system and max. 64 V in the 48 V electrical system.

Related categories: Battery isolators, relays and boat batteries

Correct installation of your boat electrics is enormously important. This starts with the correct sizing and selection of your cables with the appropriate pole terminals, fuses, relays and switches and ends with the safe storage of batteries in battery boxes, because even a 12-volt system poses considerable dangers. Many boat owners forget that even on-board batteries contain considerable amounts of energy and can deliver very high currents which, if installed incorrectly or in the event of short circuits, can lead to fire and gas development, and in the worst case to the battery bursting and leaking battery acid.

Appropriate care and maintenance is also recommended to ensure the longevity of your batteries and vehicle electrical system. With battery testers you can test the performance of your batteries and with a battery refresher you can prolong the life of your batteries. You can bring them back to life even in the event of heavy sulfation!

Customer ratings & reviews

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Harald U. on 02.10.2022

Very professional!!

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Harald U. on 02.10.2022

One word, perfect.

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Franklin W. on 02.10.2022