Blog, 25th Anniversary

While Your Boat is Stowed Away for the Winter, Don’t Forget to Check on the Battery

Nothing can spoil the early days of spring worse than launching your boat and finding out the batteries are dead. You take great care during the winter months to drydock your boat, clean the hull, clean and treat the teak, polish the chrome, remove salt residue and buildup, and more. However, if you do not take steps to also protect your boat’s batteries, you will likely not be able to enjoy your boat without replacement when the warmer temperatures arrive.

The good news is that if you take a couple of simple preventative steps, you can extend the life of your marine batteries and help make sure that everything is “ship-shape” when you are ready to launch your boat in the spring. Even if you live in the warmer states where you may not need to “winterize” your boat, it’s a good idea to still check  the battery when you know your vessel is not going to be in use for an extended period. As always, be sure to follow the manufacturer’s guidelines for battery care and handling and direct any questions to your battery professional.

Proper Storage and Charging Procedure is Key

A good step to ensuring a healthy battery for your vessel come spring is making sure it’s safely and properly prepped for its winter slumber. It’s wise to inspect cables, connections and the battery case as well as remove any dirt or corrosion on the battery terminals. If you’re using a conventional lead acid battery, make sure to water it properly by following specified measurement levels outlined by the battery manufacturer.

When you know your boat will sit idle for several months, it’s a good idea to remove the battery from the vessel and store it in a cool, dry location, where it will not be exposed to freezing temperatures that can damage the battery. With a conventional lead acid battery, store it safely in a plastic bin or on a surface that will not react with acid should the battery leak or become damaged.

If you opt to not remove the battery from your boat, you should disconnect all the terminals to avoid the battery from fully discharging. Many electronic systems can continue to draw small amounts of power from the battery, called parasitic loads, even when properly turned off.

Whether you decide to keep your battery on the boat during the off-season or stow it in a spot of its own, it should be located somewhere within easy access so that you can perform regular maintenance checks to determine the battery’s State of Charge (SOC). On a conventional flooded lead acid battery, check each cell with a hydrometer to confirm a specific gravity of 1.265-1.285 or read the voltage with a voltmeter. A voltage of 12.6V indicates a fully charged flooded battery. An Absorbed Glass Mat (AGM) battery voltage would read 12.9V or higher when fully charged.

Fully charging the battery before storing it is recommended to prevent the buildup of sulfation, which can accumulate to a point where the battery will stop working. A fully charged battery will help prevent over-discharge from parasitic loads that onboard electronic devices and accessories can cause. This can also be prevented by using a trickle charger in storage. However, the best practice is to disconnect the negative battery cables or use a battery disconnect switch to ensure that no devices are wired directly to the battery.

The “Cold” Facts

In the colder states, proper charging becomes even more important, especially in conventional batteries. The key to protecting any battery from freezing is to make sure it stays fully charged throughout winter. If the battery is used sporadically, and left to discharge during this time, the electrolyte begins to change from acid to water as the voltage declines. The more water-like the electrolyte becomes, the easier it is to freeze. A fully discharged battery can freeze at around 32°F (0°C).

Selecting a New Battery

Virtually maintenance-free ODYSSEY® Marine Dual Purpose batteries are manufactured with a military inspired design and Thin Plate Pure Lead (TPPL) technology to offer slower self-discharge, less corrosion, faster recharging and better endurance in harsh environments. They can be brought back from 20 percent SOC to better than a 90 percent SOC in about an hour, are resistant to high-impact shock, and can perform in extreme temperatures as low as -40°F (-40°C). They are designed to deliver twice the overall power and three times the life of conventional flooded lead acid batteries.

Whether you are seeking enormous cranking power to start the dual engines in your yacht or the deep cycle reserve power for all your accessories to enjoy a day of fishing, ODYSSEY® Marine Dual Purpose batteries have the power to enable you to have a worry-free day when it’s time to get back out on the water.

This year, EnerSys® marks 25 years of ODYSSEY® battery production. To follow the ODYSSEY® battery 25th Anniversary journey, visit our website at or connect with us on InstagramTwitter, and Facebook by using the hashtag #MYODYSSEY.


EnerSys, the global leader in stored energy solutions for industrial applications, manufactures and distributes energy systems solutions and motive power batteries, specialty batteries, battery chargers, power equipment, battery accessories and outdoor equipment enclosure solutions to customers worldwide. Energy Systems, which combine enclosures, power conversion, power distribution and energy storage, are used in the telecommunication, broadband and utility industries, uninterruptible power supplies and numerous applications. Motive power batteries and chargers are utilized in electric forklift trucks and other industrial electric powered vehicles requiring stored energy solutions. Specialty batteries are used in aerospace and defense applications, large over-the-road trucks, premium automotive, medical and security systems applications. EnerSys also provides aftermarket and customer support services to its customers in over 100 countries through its sales and manufacturing locations around the world. With the NorthStar acquisition, EnerSys has solidified its position as the market leader for premium Thin Plate Pure Lead batteries, which are sold across all three lines of business. More information regarding EnerSys can be found at