How Long Does a Marine Battery Last? Expert Answer

With prices of boats nowadays, it is more often than not that we buy a second hand boat.

One which comes with some extras the previous owner throws in, including the battery. Now the battery looks clean and it’s working.

Do I need a new battery? - you may ask - this one should be ok, right?

Being stranded out in lake with a dead battery is not fun. Not to mention, embarrassing. Unless you know for sure how old the battery is, you might be living on borrowed time.

 It is recommended that you either change to a new one or keep one spare for emergencies.

Whichever you decide to go with, it is important to have an idea on how long your battery will last and how you can take care of it.

How Long Does a Marine Battery Last?

marine batteries

how long a battery lasts will depend on the following factors:

Using the Right Battery

If you have been using an automotive battery and wonder why it did not last very long, you are using the wrong type of battery. 

Buying a dedicated marine battery is essential.

An automotive one may only take you so far but a well-maintained marine battery will probably last you 4-5 years from new.

Age - How Long Does a Marine Battery Last

Just as above, the older the battery, the more likely the plates will suffer from positive plate shedding.

Too much of that brown sludge at the bottom of the case is a dead giveaway that you should consider changing the battery.

Temperature & Humidity

Just like Goldilocks, too hot and too cold will wreak havoc on your battery.

 If the temperature is too cold, it will cause the positive plates inside the battery to shed or flake during charging cycles.

All that sedimentary build up and brown sludge at the bottom of the battery and can short the battery.

Too hot and the grids in the battery will expand and shrink, parts will corrode and the water in battery will evaporate.


On its own whilst in storage, the battery will continue to discharge; sometimes as much as 30% per month.

Again, if the storage is too hot or cold or too humid, it might have bearing on the discharge. If the battery is left in deep discharge until summer comes round again, it will be harder to charge and affect its life expectancy.

Incorrect Charging

Either undercharging or overcharging the battery can shorten its life expectancy.  

Undercharging the battery leads to the sulfate hardening, a process known as sulfation.

It caused false voltage readings which led to further uncharging; until the battery goes dead.

Overcharging takes the electrolyte out of the cells and can potentially cause overheating that could lead to a very dangerous situation.

Poor Maintenance

A poorly maintained marine battery will not be able to give its best. Taking shortcuts like using tap, instead of distilled water, will lead to sulfation.

A battery which is not cleaned often or have spots of corrosion can also be a hazard.

Tips on Taking Care of Your Battery

As above, there are many factors that affect the marine’s battery life.

However, there are some simple routine maintenance you can do to prolong your battery’s life.


The cold snap is here and you are done for the season. Have a thought about how to store your battery.

  If it is convenient, the best way is to disconnect and remove all your batteries and keep in somewhere cool and dry, preferably in your house.

A well-maintained battery can usually withstand low temperatures but anything below zero, there is a chance that the cells in the battery can freeze. There is a higher chance of this happening if the battery is left in the boat outside.

Shallow and Slow Charge

Having them disconnected and within easy reach means you could charge the battery sporadically - making sure it does not go below 80% discharge.

 Shallow and slow charging is a sure-fire way to prolong the lifespan of your battery.

If you keep up this full charging once a month over low season, the battery will be primed and ready when it’s time to go out to the lake again.

Lot Rot

In the case where it is not a portable battery, it is advised that you run the battery on a few small equipment to prevent what is termed as Lot Rot.

This is when the battery becomes dysfunctional due to little use.

Old and New Don’t Mix and Stick to the Same Type

While we are all about diversity and not ageist, in the world of marine batteries, old and new don’t mix.

 In a situation where you use multiple batteries, do not be tempted to mix old and new batteries together.

Their charging cycles will be different and ultimately, this will lead to the old batteries causing deterioration in the new ones.

In the case where you have to change one bad battery, it is recommended that you change the whole set. You can perhaps swap the bad battery with a good, used one but make sure it is in the same charging cycle as the rest.

As above, it is essential that you stick with one type of battery chemistry (either wet cells, gel or AGM).  Each type has different charging voltages and mixing the up can result in incorrect charging.

Good Maintenance

Give your batteries some tender, loving care and the batteries will love you back. Here you have some good maintenance routines that you should follow:

  • Store batteries in a clean, cool and dry place; ideally in an acid-proof storage box
  • Check and clean terminal connectors to make sure conductivity is at optimum
  • Remove any dust and dirt
  • Check fluid levels and top up with distilled water only
  • Test your batteries, ideally four times a year to make sure they are in good balance
  • Clean any signs of corrosion. A past of water and baking soda is non-reactive, safe and does not contain harsh chemicals. Use electrolyte grease to prevent further corrosion to the battery terminals
  • Wet cell batteries could use a ‘cleansing’ agent. This will remove the sulfate build-up on the plates

Follow the above routine periodically throughout the year.

Related Post: How To Charge A Marine Battery Properly

How Long Does a Marine Battery Last  Conclusion

So there you have it. A better understanding of the marine battery as well as diligent and due care is what you need to maintain your batteries.

A few simple rules and guidelines are all you need to prolong the life of your battery and to longer, happier days fishing. Ta-da!

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