Helping Your Boat Battery Survive Winter Storage

Posted by at 11:10AM - Comments: (6)

For many of us, it's that time of year when we are putting our boats to bed for the winter, or at least getting ready. With that in mind (and print deadlines looming!), I'm reviving a post from 2011, covering the basics of battery storage. If you really want to get into the nitty gritty of battery selection and system design, check out our e-book series on electrical systems, which has a section dedicated to 12-volt batteries and battery accessories. 

Few things are more disappointing than coming back to your boat in the spring and discovering that one or more of your boat’s batteries is dead. You haven’t even started sailing, and already you’re facing a hefty bill. Many times, a dead battery can be resuscitated to near its initial capacity, but it's best to avoid the problem in the first place.

Practical Sailor puts marine batteries through multiple charge and discharge cycles during testing.

If you put your boat to bed recently and haven’t yet checked your batteries’ state of charge, now is a good time to do it. Ideally, you should bring a stored battery up to full charge at least once a month. So long as you keep your batteries fully charged, you shouldn’t have to worry about electrolyte freezing. A fully charged, lead-acid battery will withstand temperatures of 75 degrees below zero without freezing. However, electrolyte in a discharged battery will start freezing at 32 degrees, just like water. Once the electrolyte freezes, you can pretty much kiss your battery goodbye.

If you haven’t put much thought into storing your battery for the winter yet, don't delay any longer. The batteries should be removed from the boat and stored in a cool place that does not drop too far below freezing. A basement or garage is fine. Today’s batteries can be safely stored on a concrete floor without risk of discharge, but it’s a good idea to insulate them on a block of wood anyway—if only for peace of mind. You can keep house batteries on the boat, but if you do, you should take the usual winterizing steps—cleaning the battery top and battery posts, filling the electrolyte, eliminating any loads that may discharge the battery—and checking voltage and recharging on a monthly basis.

There are a few ways to check battery state. The more common methods of checking battery state are using a digital or expanded-scale voltage meter to check open-circuit voltage or, on wet-cell batteries, using a hydrometer to check the electolyte's specific gravity. In either case, you need to make sure the battery’s electrolyte is stabilized, otherwise you may get misleading results. By letting a battery rest for an hour or two after recharging—or after being subjected to discharge loads—the electrolyte is usually fairly stable. Typically, the electrolyte will be stabilized after only a few hours (or even minutes) of rest, but in some cases it may take up to 24 hours, even longer in some gel batteries.

If you have serious concerns about your battery’s condition, you should consider having it load-tested at a reliable battery service center. Big boatyards, most automotive repair shops, and battery dealers will have a heavy-duty load tester suitable for high-capacity marine 12-volt batteries. Owners of inboard diesel engines can simulate a load test, a process that is described in Nigel Calder’s "Boatowners Mechanical and Electrical Manual." Calder also describes how to compensate for temperature when checking for battery state and offers a few options for reviving “bad” batteries back to near capacity, tricks that can save you hundreds of dollars that you might have spent on a new battery you didn’t need.

For more details on battery storage this winter, check out our online article on battery care. If you do find yourself shopping for a battery this winter, two articles worth looking at are our recent test of sealed batteries and Andy O’Grady’s article on extending the life of wet cell batteries. Finally, if you are in the market for a new inverter charger, PS recently reviewed the best of the bunch.

Comments (6)

Looks like you've included some of the old wives' tail precautions (putting the batteries on a block of wood off the concrete). The best thing foe long term storage of batteries is cold. They do not discharge as fast. As temps usually stay below freezing through the winter on western Lake Superior, my batteries never need charging when kept on the boat (on the hard) and after more than 3 years, still have 12.8 volts by springtime. No backaches or hernias lifting batteries on and off the boat, either.

Posted by: Raymond S | November 10, 2014 9:44 AM    Report this comment

Over the last twenty years we have had four different boats. We have had a variety of batteries from flooded 12V group 27 & 6V Golf Cart batteries to our present 12V group 27 Gel batteries.
All of them I have left on the boat. We charged them in the fall and disconnected the cables. top of batteries were clean. No dirt. Never lost a battery and were always 50% charged or better in the spring. Gel's are always 90%+ charged in the spring.
Charged maybe late october and hooked back up in April
Located on Lake Huron.

I read some where that a battery looses considerably less charge at 0C then it does at 20C

Posted by: wavelength | January 12, 2012 3:50 PM    Report this comment

For 9 years now I've connected a flexible 1/2 watt solar panel to one battery and left the battery switch on "both", hung the panel on the outside of my boat cover and faced the panel generally south or west. The panel has kept both of my AGM batteries at 13.5 volts all winter here on the Hudson River. I've never taken the batteries off the boat, or even disconnected them in 9 years.

Posted by: Douglas M | December 29, 2011 9:25 PM    Report this comment

I leave my boat for the winter in Glades Boat Storage, Florida, on the hard for about six months. I have no electrical power but use a simple 15 watt solar panel with a regulator - a cheap one - and it seems to keep my battery bank up to snuff and the bilge dry. I should probably use a more sophisticated regulator. Anyone have any info on suitable regulators.

PS I do the same thing with my car battery in Northern Ontario with a much smaller solar array and no regulator and the battery appears to cope with it given the winter sun.

Posted by: jean k | December 29, 2011 8:21 PM    Report this comment

If you have 117v to your boat, always use a good trickle battery charger.
Do not try to save money on this item.
Do not use a car charger!
Also check your electolyte level twice a year.
A load tester is a good investment.
A digital meter is also a great tester.

Posted by: Ralph S | December 29, 2011 12:03 PM    Report this comment

The article mentions load testing the batteries. I was having trouble with what appeared to be insufficient battery capacity and the marina mentioned load testing. I was put off a little knowing how involved load testing a submarine battery was. It is a simple meter connected to both battery terminals. Took me about 3 minutes once the batteries were disconnected from the boat systems. Seems like load testing should be a part of commissioning every year.

Posted by: THEODORE L RICE | December 29, 2011 8:07 AM    Report this comment

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