Marine Battery Voltage Chart

Marine batteries are crucial components of your boat’s electrical system, powering everything from the engine starter to the radio and navigation system. However, to ensure that your battery is functioning properly it is important to monitor its voltage regularly. By understanding the voltage chart for marine batteries, you can get a clearer picture of your battery’s health, how to charge it effectively, and when it’s time for a replacement. In this article, we’ll explore the information and guidance you need to maintain your marine battery and keep your boat running smoothly.

Marine Battery Voltage Chart

State of Charge Specific Gravity (25°C) Voltage
100% 1.265 12.70
75% 1.225 12.50
50% 1.190 12.32
25% 1.155 12.20
Discharged 1.120 12.00

How many volts should a marine battery have?

The ideal voltage for a fully charged marine battery is 12.6 volts or above. This voltage is measured when the battery is not in use and is known as the “open cell” or “resting” voltage.

What voltage is too low for a 12 volt marine battery?

A voltage of 11 volts or below is considered too low for a 12 volt marine battery. At this point, the battery is considered dead or deeply discharged, and any additional use can cause permanent damage to the battery.

Is 12.5 volts OK for marine battery?

Yes, a voltage of 12.5 volts is considered acceptable for a marine battery, but it does not indicate a fully charged battery. This voltage reading means that the battery is only charged to about 75% of its capacity.

How do I know if my marine battery is bad?

If you suspect that your marine battery may be bad, there are several indicators to look for. One of the most common is a voltage reading significantly below 12 volts when the battery is not in use. Additional signs of a failing battery include slow cranking, dimming lights, and difficulty starting the engine.


Monitoring and understanding your marine battery’s voltage is essential for maintaining its health and performance. By regularly checking the voltage and charging the battery as needed, you can extend its lifespan and prevent unexpected breakdowns on the water. If you suspect that your battery is failing, it is always a good idea to replace it sooner rather than later to avoid potentially dangerous situations.

About the author, Phil Borges

Phil Borges is a battery aficionado. He's written extensively about batteries, and he loves nothing more than discussing the latest innovations in the industry. He has a deep understanding of how batteries work, and he's always on the lookout for new ways to improve their performance.