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What Should The Voltage Be On a 12-Volt Marine Battery?

the voltage on a 12-volt marine battery

Knowing the correct voltage for your battery is as important as knowing what bait to use for the type of fish you are trying to catch.

We all remember the story of Goldie Locks and The Three Bears. “This porridge is too hot. This porridge is too cold. This porridge is just right!”

Well, the same holds true for your 12-volt marine battery. Without the proper amount of voltage, your battery will not be just right. Worse yet, you may find yourself stranded out in the water, with a motor that won’t start.

Let’s take a look at a 12-volt marine battery, and see what voltage levels are good and bad.

What Voltage Should A 12 Volt Battery Have?

Optima Digital 400 12V Performance Maintainer and Battery Charger

So what voltage should a 12 -volt marine battery have? The accepted standard is 12.6 volts.

To achieve this voltage level, consider obtaining the Optima 12 volt digital 400 charger . This charger keeps the battery charge level automatically. It includes a gauge and an LCD screen. This charger is acclaimed for its ability to recharge batteries, even dead batteries that other chargers have been unable to regenerate.

Another popular charger to keep your 12- volt marine battery at the correct charge level is the Optima 1200 charger. This charger is ideal for flooded and high-performance batteries. Its interface includes charging levels, fill rate, mode settings, and fault messages.

The one you need will depend on the type of battery you have and the sophistication of the interface you want. If you typically troll at slow speeds and have plenty of time for reading the interface, you may consider the 12 -volt digital 400 chargers. 

If you accelerate to high speeds, the Optima 1200 charger may be a better choice. This will give you access to more information more quickly. 

Of course, the amount of wake you encounter is also part of your decision. Weather conditions also affect your ability to monitor your battery charge. The smoothness, or roughness, of the tides, is another variable.

So, know the conditions you are heading in, and know the likelihood that those conditions will change according to the weather forecast. The most important factor is to keep your battery charged to the 12.6- volt level. Both of these chargers will get the job done.

Fully Charged Voltage

How to Test your Boat Battery Voltage with a Multimeter!

The matter of a fully charged marine battery can be somewhat confusing. Why not just charge the battery until it is full? Wouldn’t this indicate the best charge level?

Unfortunately, it would not. This is because you want the battery to maintain its optimum level of electrolytes. You never want to diminish electrolytes.

Overcharging the battery will boil away electrolytes, and diminishing the electrolytes will shorten the battery’s life.

So, to maintain the charge, you want to keep your marine battery between 13.2 and13.4 volts. You want the battery to settle in at 12.7 volts, which it will if your initial reading is between 13.2 and 13.4 volts. It may dip to 12.6 volts, which is also acceptable.

If you have a lithium battery, strive for 13.4 volts. This will settle in at 12.8. An SLA battery should initially read 13.1 before settling in at 12 volts. 

Regardless of the type of marine battery you have, by avoiding overcharge, you will extend the life of your battery. To get the best performance and life from your battery, it is good to have a maintenance plan.

First, know the optimum voltage level of your battery. If you have a heavy load, consider using more than one battery to lessen the battery workload. Measure the space available in your battery compartment to determine how many batteries you can utilize. Remember, the batteries may expand during use, so leave adequate space between the batteries.

Advice: Managing batteries on a boat

Next, choose the best battery models. When replacing a battery, select a similar-sized model. Try to choose a unit that supplies a similar amount of power as the battery you are replacing.

Finally, choose terminals carefully. Consider the cable connections you prefer and select terminals that fit well with those cables. Loose connections mean wasted power.

The performance of your battery goes beyond the optimum fully charged voltage level. It has to do with the workload and with the conditions the battery is working under.

What Voltage Is Too Low?

You don’t want a battery that is undercharged, as well. You want your engine to start and your onboard components to continue working. So what voltage level is too low?

Your first concern is avoiding damage to the battery cells. Avoid using a battery with 12.2 volts, or less. This indicates a weak battery. 

Damage can begin when the voltage goes lower than 11.8. That is why battery cutoffs prevent voltage from going below this level.

It is good to understand the state of your 12-volt battery based on the current percentage of charge level. A battery with 12.6 volts is considered to be fully charged.

A battery with 12.5 volts is 90% charged. The 80% charge level is 12.42 volts. The 70% level is 12.3 volts.

Sixty percent is 12.2. Fifty percent is 12.06 volts. Forty percent is 11.9. Thirty percent is 11.75. Twenty percent is 11.58. Ten percent is 11.31. 

Finally, if a 12-volt battery is charged to 10.5 volts or less, it is considered as not being charged, or dead.

Battery manufacturers typically recommend keeping your battery above the fifty percent level. According to our above levels, that would be 12.06 volts.

Otherwise, you can not expect your battery to have a long life. The more you run down your battery, the fewer charge cycles you can expect to get.

So avoid undercharging your 12-volt battery, unless you enjoy trips back to the marine store and laying out money for a new one.

Consider time spent transporting the new battery to your boat and reinstalling it. That is time you could be spending out on the water.

Charging And Battery Health

testing battery voltage with a voltmeter

To determine the health of your marine battery, you need to determine if it has a proper voltage level and also does a gravity test. If your battery is healthy and merely needs charging, you can do multi-stage battery charging and three-stage battery charging. 

A gravity test is important to analyze the health of a battery. Voltmeters and hydrometers can be used to get an accurate reading. The combination of these results will tell you how healthy your battery is.

First, be sure to charge the battery fully. A fully charged 12-volt battery will have 14.2 to 14.4 Volts of Direct Current, or VDC. This indicates that the volts are constant, instead of alternating. 

Your battery reading will reflect constant current, instead of changing back and forth from positive current to negative current. 

Multi-Stage Battery Charging, by definition, is “the application of specific controlled charging stages to maximize battery charge, health and life span,” according to Generation Solar.

How to - Charge and maintain a battery

In this charging method, the current is constantly charging. It is at a uniform pace. It does not consider the current state of the battery or the current level of charge of the battery.

The first stage is the Bulk Stage. The battery is charged to the greatest voltage level possible. It is a constant charge instead of a variable one.

The next stage is the Absorption Stage. The battery charges until it reaches a preselected point. When this absorb charging point is reached. The voltage level is held constant. The current level then begins to decrease. It decreases to a level that is selected beforehand.

This is completed in somewhere between two and five hours. The time taken is called the Absorb Time. This is important because the battery is typically brought to 95% charge.

At this point, the battery charge changes to the Float Stage. This brings the battery charge up to 100% charge.

Float charge is commonly referred to as a trickle charge. This process is also referred to as three-stage charge. In comparison, a two-stage charge would not include the Float Stage.

Determining if your marine battery is healthy is easy if you use a voltmeter and a hydrometer. The voltmeter tells you how many volts your battery has. You are looking for a measurement of 12.6 volts or higher. 

You obtain the measurement by connecting the positive voltmeter wire to the positive battery terminal and then connecting the negative voltmeter wire to the negative battery terminal.

A hydrometer measures the characteristics of the liquid inside your battery. It tells you if the individual battery cells are good. Specifically, it measures the gravity of the battery.

to check the gravity of the battery with a hydrometer

Gravity compares the weight of the electrolytes inside the battery cells to the weight of an equal amount of water.

The result is given as a ratio. You are looking for a hydrometer reading of 1.285 on each cell. Refer to your hydrometer manual to properly use your particular unit.

If your voltmeter and hydrometer readings both yield these recommended results, you can rest assured that you have a healthy battery.

With the knowledge that your battery is healthy, you can be confident that your engine will start and your navigational instruments will have the power to work properly.


Knowing the proper charge level on a 12 -volt marine battery is critical to getting the maximum life span from your battery. We have seen that the voltage on a 12-volt battery should be 12.6 or higher.

A fully charged battery can reach over 14 volts. A voltage level below 12.6 is a concern, and a level of 12.2 volts is a bad sign. 

To measure your charging, use the multi-stage or three-stage charging methods. Your battery is healthy if it registers the proper volts when using a voltmeter. This, combined with an acceptable hydrometer reading, indicates a healthy battery.

With a healthy battery and the right bait, of course, you can anticipate a successful day of fishing!