Marine battery monitors are simple electric and electronic devices that monitor various parameters of marine battery and display them in a simple and readable manner. Built-in alarms can warn the user that certain parameters are out of desired range and can save the day. And often much more ...

marine battery monitor 1

Marine Battery Monitor's Features

Marine battery monitors should be integral part of the electric system of any boat with permanent main battery installation.

Even the smaller boats that uses marine batteries periodically should have simple battery monitor, just in case - in such situations, use of marine battery box with built-in battery monitor is highly recommended.

Most important battery parameter to monitor is voltage. Other important parameters include current, energy, power, temperature and similar.

marine battery monitor 2Hence, all battery monitors measure battery voltage and present that information in several ways: LCD, LED or similar digital displays or using status LEDs. To alarm the user, flashing display, flashing LEDs and audio alarms are used.

Most battery monitors are designed for 12V or 24V line voltages, but nowadays it is fairly easy to find suitable battery monitor for other voltages.

In order to measure the voltage, simply connect the monitor to the boat electric system - ground to the ground (or 'minus') and live wire to the live wire (to the '12V' or '24V' wires) and that is it.

When not in use, to avoid discharging the battery, battery monitors should be turned off, or even plugged out of boat electric system.

Measuring the current is a little bit more complicated - in order to measure the current, in most cases, one must insert 'shunt' in the electric system, where current should be measured. There are other ways of measuring the line current, but this one is most common, especially for currents below 100A. For stronger currents, clamp meters of various types (for example, with Hall magnetic sensor) are used.

Current can be measured in various parts of the electric system, it doesn't have to be the current of the battery itself - for example, one can measure current and line voltage when using electric trolling motor powered by dual-purpose main battery. When voltage drops below certain level (for example, slightly above voltage required for safe starting of the main boat engines), trolling should be stopped.

Anyway, when current is measured, it is fairly easy to calculate power (voltage x current) and spent energy (voltage x current x time).

Since charging and discharging of marine battery can increase its temperature, measuring battery's temperature can be a good idea. It is done relatively simply by using temperature sensor which is usually glued on the battery using duct tape (comes with the sensor) and connecting the sensor's wires with the battery monitor.

What Battery Monitor to Use?

marine battery monitor 3Main battery monitor must be positioned right after the battery and it must directly measure at least battery voltage. Measuring battery current is not so important, but your circuit breakers must be dimensioned properly.

If you experience any issue with your battery and you suspect that something is discharging the battery, ask a professional for help. Marine batteries can supply huge currents and can make a lots of damage. After all, they are not cheap.

If your boat has battery chargers like solar panels and/or wind turbine(s), then your charging controller already has a means to display status of your battery. Some more advanced models even use GSM modules to send information directly to the smartphone or iPhone.

Using electric trolling motor on a small boat or kayak is recommended in combination with a good marine battery box and built-in battery monitor - nobody wants to row back, right? :)


Marine battery is valuable asset on the boat and monitoring its condition and health is very important. Even the simplest voltmeter which costs few dollars/euros can save you from lots of troubles.

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