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How Can You Tell How Old a Marine Battery Is?

How Can You Tell How Old a Marine Battery Is?

Every boater should know how old his or her marine batteries are.

The batteries are arguably the most important items on your boat— they give your boat life. It is necessary to know the age of your batteries so you can properly maintain your boat’s electrical system and help prevent any issues.

No boater wants to experience any unexpected issues while out on the water. 

Luckily, you can easily find out the age of your marine batteries.

Before you learn how to find that information, let’s talk about how long you can expect your batteries to last, and also what symptoms may signal a dying battery.

What is the Average Life of a Marine Battery?

Miady 12V 36Ah Lithium Phosphate Battery for Marine Applications

You can expect your batteries to last roughly 4-6 years, assuming you are properly maintaining them.

Many people overlook their batteries when they consider boat maintenance, but this is a vital portion of your overall maintenance. Boaters can easily notice visible signs such as corrosion and potential leaks, but there are other things to consider as well. 

How you store your batteries will play a tremendous part in keeping your batteries healthy. You want to store your batteries in a cool, dry place, and make sure they do not hold a charge that is either above or below the recommended level. 

Therefore, it is necessary to test your batteries from time to time

If you have taken your batteries off the charger and they are reading improper levels, this could be a sign that your batteries are aging. However, if they are relatively new batteries, then you should still consider replacing them.

Your batteries should read at least 12.4V after charging.

batteries read at least 12.4V after charging

Overcharging can also be an issue if you leave your batteries on the charger for too long. Charging times may vary, depending on the quality and type of charger you are using.

If you need to replace any batteries, make sure you check for any warranties that might still be active.

Now that you know the average life of your batteries and have learned a few ways to preserve that life, let’s learn how you can find out how old your batteries are.

How Can You Tell How Old a Marine Battery Is?

age of marine battery

Many battery manufacturers include a date on their batteries, and this date will let you know when your batteries were manufactured. This will be the case for all your marine batteries, including deep-cycle batteries.

This date may be engraved on the battery, or there might be a sticker or label. 

However, you may not see the date when you go to look for it.

Many times, the dates are shown as a certain code. Each code is made up of letters and numbers, and each digit corresponds to a part of the date.

For example, one digit might tell you the year. Another digit may tell you the month. 

Let’s take a look at a few popular marine battery brands and find out which methods they use to show the dates.


Interstate Batteries 12V 35Ah Deep Cycle Battery

Interstate batteries will have a code etched into the battery casing. Look at the top of your battery and try to find a code containing either four or five digits.

It is recommended to look for this code around the corners of your battery, or even on your battery’s positive terminal.

It may help to write this code somewhere because you will need to decipher it.

Your first digit will be a letter, and this letter will correspond to the month. If your letter is the third letter of the alphabet, then it will correspond to the third month.

For example, “D” is the fourth letter of the alphabet. Therefore, “D” would correspond to the fourth month (April).

If your code started with a “U” then you will need to ignore it and begin this process using the next digit, which would be another letter.

The second digit (or third digit, if your code started with a “U”) will be a number. This number corresponds to the last number in a year. 

The last digit of the year 2015 is a “5.” If your second digit is a “5,” it could correspond to the year 2015. 

However, the “5” could also correspond to the year 2005. You will have to use your best judgment on which year is correct.

Interstate also puts a second code on their batteries, but only if it has been in stock for three months. They recharge the battery after it has been sitting this long and the second date will correspond to the date they recharged the battery.

This will be a similar code, and you decipher it the same way as your other code.


Everstart battery age

Everstart also uses a code to note the date on their batteries. You will have to decipher this code also.

Your battery may have the code etched into the battery casing, but you may also find the code on a label somewhere on the battery.

Look for a code that has a letter for the first digit and a number for the second digit. 

Once you find this code, decipher it using the same method described above for the Interstate batteries. 

The letter will correspond to the month, while the number corresponds to the year.


How Old Is Your Car Battery? (Reading Battery Date Codes)

It is very easy to find the date on Duralast batteries. Normally there will be a sticker somewhere on the battery that notes the date.

That’s right– the actual date is noted. There won’t be a code to decipher.

You will probably find the sticker on the top or sides of the battery. The first two digits represent the month, while the last two digits represent the last two digits of the year.

Example: 03/18 represents March 2018.


age of DieHard battery

Dates on DieHard batteries are similar to the Interstate and Everstart batteries.

You will find a code on your battery that will need to be deciphered. The first digit will be a letter that corresponds to the month, and the second digit will be a number that corresponds to the year (use the same method as the other batteries to decipher).

If the code is not etched into your battery, there should be a label on one of the sides that contains the code. 


Optima Batteries 8004-003 34/78 RedTop Starting Battery

Optima batteries will be similar to Duralast– the date should be noted clearly on a sticker (no code to decipher). 

The sticker will most likely be at the top of your battery.

If your battery is missing the sticker, you can also use the digits on the barcode. The first digit on the barcode will correspond to the last digit in the year it was made. If you add the next three digits together, that will tell you which day of the year it was made.

Example: If your three digits all add up to 72, that will be the 72nd day of the year- roughly mid-March.


Odyssey 31M-PC2150ST-M Trolling Thunder Marine Dual Purpose Battery

The Odyssey batteries will have a code similar to some of the other batteries. Use the same method to decipher the code– the first digit is a letter corresponding to the month, with the second digit being a number that corresponds to the year.

You should be able to find this code on a label on the back of your battery.


Deka Power Sports ETX20L Battery

Deka is another brand that uses a code for the date. Once again, use the same method to decipher it– the letter corresponds to the month and the number corresponds to the year.

However, Deka chooses to skip the letter “I” in the first digit. September will be noted by the letter “J” instead.

The code should be on a sticker somewhere, or it may be etched into the side of your battery.


It is important to have healthy working batteries on your boat. Now that you know how to determine the age of your marine batteries, you can decide if now is a good time to go ahead and replace them. 

If you decide it’s too soon to replace them, you can at least have a good idea of how much longer you may have until you need to start considering replacing them.

The age is just a number– there is a possibility your battery can start exhibiting signs of trouble before the average age range. In that case, you should go ahead and replace it or look into the problem.

In the meantime, make sure you take care of your batteries and always include your batteries in your overall boat maintenance routine.