How long do boat batteries last?

How long do boat batteries last?  

There's nothing worse than a flat battery out on the water. It can really put a real DAMPENER on the mood. To wrap your head around how long a boat battery will last off one charge can be a little tricky, but we will break down the basics in this blog. The general rule of thumb for most marine batteries, they are generally charged by your outboards alternator which provides a consistent and reliable charge while the outboard motor is running. This will help prolong the lifespan of your battery, meaning you can enjoy the use of your 12v marine accessories and a day out on the water. Understanding just how long your boat battery will last will also come down to how often you are using your boat. If your boat is stored for a certain period like to your car battery this will lead to the battery discharging and going flat. However, it is good practice to have your batteries replaced every 3-4 years depending on use and maintenance.  

How long does it take to charge a marine battery?  

Now this really comes down to the size of your marine batteries CCA and Amperage which can be found in most cases on the battery casing or labels. Most Marine batteries are measured in CCA or commonly known as “Cold Cranking Amps.” This is a measure in what is required to talk to your outboard’s computer allowing it to start your motor. Having a quality/ high amperage Marine charger will not only allow you to charge your battery faster but also being able to do a maintenance charge ensuring your boat battery is in its best tip top condition. That’s why we recommend the 20-amp Pro Mariner marine battery charger for the fastest possible charge, especially when you are working on your boat at home or if it is being stored for a long time. 

Generally, the rule for boat batteries when charging is for ever Amp hour your battery is to the size of your battery charger’s amp hour will take roughly an hour to charge.  

i.e. 20amp battery charger - charging a 120amp battery allow 6-8hrs for a full cycle charge.  

How do boat batteries charge? 

One thing of note is that marine batteries are not measured in amps, they are measured in CCA or ‘Cold Cranking Amps’. What this means is the cranking power to turn over your outboard motor, is like the starter battery on your car. Therefore, if you plan on using it to run your appliances it's important to measure how many amps your accessories will draw over the period of 6 hours - give or take. If you have a sounder, GPS and lights installed to run of the main cranking battery of your boat then you are looking at upwards of 1-5amps per hour. Over 6 hours that will be worse case scenario you will use about 30a over the 6 hours, you’ll be leaving your starter battery at about half charge. This is not a recommend way of running accessories as you need at least 80 percent on your start battery to crank the motor over. Therefore, it is highly recommended if you are to run the above accessories or more, then installing a dual battery system is the way to go.  

For the most efficient possible charging we highly recommend installing a quality onboard marine charger that is permanently fixed to inside the hull. You can find the full range of marine electronics accessories here: