Helping Your Boat Battery Survive Winter Storage

Posted by at 11:10AM - Comments: (19)

 

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—this is not always possible, and may not be necessary so long as you start off with a full charge. If you keep your batteries fully charged, you shouldn’t have to worry about electrolyte freezing, and you'll reduce the risk of diminishing the battery's capacity. A fully charged, lead-acid battery will withstand temperatures of 75 degrees below zero without freezing. However, electrolyte in a fully discharged battery can 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 protecting your battery for the winter yet, don't delay any longer. If the batteries are removed from the boat, store them 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, and 12 tips on extending AGM battery life. Owners of AGM batteries will be especially interestd in our in-depth look at how repeated incomplete charge cycles can reduce the battery's capacity. If you do find yourself shopping for a battery this winter, two other articles worth looking at are our test of sealed batteries and Andy O’Grady’s article on extending the life of wet cell batteries like the popular Trojan 6-volts. Finally, if you are in the market for a new inverter charger or battery monitor, PS reviewed the best of the bunch.

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. [Editor's note 1/18/18: This post has been edited to clarify that leaving the battery on the boat is perfectly acceptable and common practice.]

Comments (19)

Thank you PS for printing all of the comments. There is more good information in the comments than the original article. I can't remember exactly when I began my original subscription to PS but I believe it was in the early 1980's. Since then, and particularly in the digital age, I've noticed a significant shift from quality to quantity in your content. Perhaps a return to less frequent but well researched articles would be welcomed by your readers?

Posted by: ventura multihulls | January 24, 2018 7:31 AM    Report this comment

The only reason I can think of to put a flooded LA battery on boards instead of directly on concrete is temperature. If cold on bottom, and warm near the top, this will worsen the tendency for denser, stronger acid to settle lower, leaving upper plates exposed to weaker acid. Without regular charging (especially a full absorb cycle) to mix the stratified electrolyte, the upper plates could be more prone to permanent damages from hardened sulfate.

As others noted, self discharge happens much more slowly in the cold. A fully charged, uniformly cold battery is good to ~70degree below zero. Unless you're on the hard in Antarctica, not likely to be a problem.

As well as my boat, I also have an off-grid cabin with a fairly large battery/solar system. Hauling a dozen 150# L16s out in the fall is not going to happen. Just checked on them after a long spell of sub-zero F temps, and they're fine.

Posted by: %2B1 for yellow - example 2 | January 21, 2018 1:28 PM    Report this comment

The only reason I can think of to put a flooded LA battery on boards instead of directly on concrete is temperature. If cold on bottom, and warm near the top, this will worsen the tendency for denser, stronger acid to settle lower, leaving upper plates exposed to weaker acid. Without regular charging (especially a full absorb cycle) to mix the stratified electrolyte, the upper plates could be more prone to permanent damages from hardened sulfate.

As others noted, self discharge happens much more slowly in the cold. A fully charged, uniformly cold battery is good to ~70degree below zero. Unless you're on the hard in Antarctica, not likely to be a problem.

As well as my boat, I also have an off-grid cabin with a fairly large battery/solar system. Hauling a dozen 150# L16s out in the fall is not going to happen. Just checked on them after a long spell of sub-zero F temps, and they're fine.

Posted by: %2B1 for yellow - example 2 | January 21, 2018 1:27 PM    Report this comment

I agree with many/most of the other comments - fully charged batteries don't need to be taken home plus, the weight prevents removal in many cases. My batteries are size 4D, weighing in at 115 lbs each. Once on the hard it would be a serious safety issue to try to manhandle them onto the rear platform and then down a ladder.
It has seemed to me for several years now that PS has a focus on smaller boats (in this case with smaller batteries) such as my first boat, a C&C 29MkII. But, when I look around my marina, other marinas and harbors in the area, and talk to sailing friends, I hear a lot about 36 to 42 foot boats. The old C&Cs etc might have been great designs, but for goodness sake, today we are all looking at bigger boats and less maintenance. So, in my case its a twenty year old Catalina 380, and with friends its 36 to 42 foot Beneteaus and Catalinas with the occasional newer model Tartan and Saber. My own projects which I do myself include rigging replacements, new electronics, new cabin sole, wiring upgrades, solar panel installation, etc. I'm finding less and less in PS, great concept though it is, that apply to me. This re-post of an older battery article just reinforced that PS is standing still.

Posted by: Tom T | January 19, 2018 11:43 AM    Report this comment

Are you kidding?

This article is atrocious!

There is absolutely no advantage to storing batteries on wood. Hasn't been for a long, long, long time; ever since battery cases have been made of rubber or plastic, certainly for as long as I've been alive.

There is far more risk to person and vessel, slugging batteries on an off a boat, vs just leaving them in place, topped up, fully charged, and after passing load test, negative terminals disconnected.

Leaving batteries on a charger is not good practice. The regular shore power charger or larger solar charger system should not be left connected. In the highly unlikely event of a battery short on a high capacity charger, thermal runaway and a boat fire could occur.

When batteries are left connected, if there is a parasitic load and the power/charger connection is lost, and/or if one battery fails unexpectedly, it will discharge all parallel connected batteries, and the whole bank could freeze and bust. If one insists on leaving batteries on float, it should be a very low current limited charger (~2A max).

Leaving a charger unattended on the boat over the winter may violate marina rules and regs and your boat insurance policy.

Just because one has gotten away with bad practice for a length of time, doesn't make it good practice, just because the boat hasn't burned...YET.

Attempting to move batteries needlessly can result in:

1. Personal injury - back, hernia, falling off a ladder while trying to manhandle batteries, slipping on a dock, dropping on a toe, splashing spilled electrolyte in eyes and on skin
.
2. Property damage - drop a battery and floors, woodwork, or fibreglass can be damaged, carpets can be damaged by spilled electrolyte (boat or car), broken battery casing.

If one hasn't suffered damage or injury taking them off the boat, well, there's always the chance when loading them into the house from the trunk, or when loading them back into the car, or back onto the boat.

Total Nonsense!

Another reason for leaving batteries aboard is if one should want to do anything requiring lights or power during the off-season, like maybe for doing some maintenance.

The author of the article above is so ill-informed, this should never have been published and should be removed. It is an embarrassment to Practical Sailor, a laugh to anyone who knows anything about batteries, and is a disservice to anyone who doesn't.

Rod Brandon
Marine Service Provider
Sheen Marine

Posted by: Oh for | January 19, 2018 7:47 AM    Report this comment

I can only reinforce the comments above regarding the old wives' tales about storing batteries off-boat and concrete floors. After 35 years of on-board storage of fully charged and properly filled batteries over 5 months of cold Canadian winters on the north shore of Lake Ontario I've not been disappointed with discharged or freeze-damaged cells in the spring.
Yes, dubious batteries were replaced before winter's onset to avoid further damage and false economy and with a 3 stage marine charger I usually get at least 5 years out of a "retail" marine brand "deep cycle" battery - actually a hybrid start/deep, made by a national manufacturer under a 'house' label.
As for the wood-on-concrete storage!!! Lets get rid of that myth forever. Neither a cold block of wood nor a cold concrete floor will contribute to a healthy charged battery.
For sure I'm not speaking from experience in that regard, because I have never off-loaded batteries and as I age, I'm not likely to start doing so.

Serving as a knowledgeable resource to my technophobe neighbours, I would also suggest that most spring-time battery problems are purely poor maintenance or aspirational optimism; i.e. a battery reading 12v after 24 hours of charging is a DEAD battery; go spend some money!!

Posted by: PeacheyKeen | January 18, 2018 1:33 PM    Report this comment

Solar trickle charging will keep your batteries at full charge and will avoid sulfation. I'm using a cheap panel from Harbor Freight which while not suitable for cruising is good enough for the winter layup.

Using a shore charger, even a big one, may take hours to bring the house batteries to full charge as the charging rate slows as the battery reaches full charge. Leaving a battery partially charged for long periods causes sulfation (as reported in other PS articles) and kills batteries. That is why a trickle charger continuously connected is better than a once a month top up. A trickle charger is needed even if you take the batteries home.

If you don't have a trickle charger, then the battery cables should be disconnected to avoid any small (parasitic) loads that are common on boats. AGM batteries self-discharge at a much lower rate than wet cells.

Posted by: Boston Barry | January 18, 2018 12:39 PM    Report this comment

This article seems a bit misaligned from today's practices, I suggest removing the article.

Posted by: GrandpaSteve | January 18, 2018 11:45 AM    Report this comment

I too disagree with this article My five group 31 Life Line AGM batteries do not go South in the winter nor do they get of the boat. This article is a black eye for PS The writer is not well informed.

On another matter I was shocked to read about Saga and Allan Poole. The Saga was a a piece of #####. Too bad Bob Perry put his name on it! You need to do your home work. Owners will tell you how great the boat was because they want to sell you the boat. You might also question why Allan Poole has earned such a bad reputation. You may find this offensive, but it is honest.

Posted by: Outbound4r6 | January 18, 2018 11:38 AM    Report this comment

I too disagree with this article My five group 31 Life Line AGM batteries do not go South in the winter nor do they get of the boat. This article is a black eye for PS The writer is not well informed.

On another matter I was shocked to read about Saga and Allan Poole. The Saga was a a piece of #####. Too bad Bob Perry put his name on it! You need to do your home work. Owners will tell you how great the boat was because they want to sell you the boat. You might also question why Allan Poole has earned such a bad reputation. You may find this offensive, but it is honest.

Posted by: Outbound4r6 | January 18, 2018 11:37 AM    Report this comment

I have always counted on Practical Sailor to provide objective, science based, tested information but that doesn't appear to be the case for this article. A fully charged lead acid battery at or near 1.26 specific gravity will not be damaged at all by even extreme winter conditions. (As cold as -34C in my case on Georgian Bay). A charged lead acid battery will self discharge far less in cold temperature than in warm or hot conditions. I heartily endorse the reference to Mainesail's testing that another commenter referenced below. Although I think there is a good amount of data, both real (Mainesails's write up) and anecdotal (my experience and that of other commenters) supporting leaving batteries in place over the winter, perhaps this is a topic that could be scientifically evaluated by cold climate contributors for Practical Sailor in a future article. In the mean time, it may be prudent to remove this article and related links to maintain PS's otherwise good reputation for fact based data on sailing equipment and maintenance practices.

Posted by: Dave S | January 18, 2018 10:16 AM    Report this comment

So...I have two D4's in my Catalina 36 MkII. Removing them is a Herculean task, so I have always charged them to full capacity, disconnected all terminals, and let them lie in the boat, which is stored covered and on the hard each winter. So far, so good. I am hoping to find around 13.5 volts remaining this April (2018) when I get back on the boat and get it ready to splash in the Spring!

Posted by: tomsailscssc@gmail.com | January 18, 2018 9:45 AM    Report this comment

Wrestle 100's of pounds of batteries out of boat for no reason and store on blocks of wood... LOL! Who's writing these?

For actual empirical data on battery discharge over the winter months and how batteries should be stored: www.pbase.com/mainecruising/self_discharge

Posted by: Hovertank | January 18, 2018 9:19 AM    Report this comment

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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