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Posted by on Nov 3, 2010 in Boat Maintenance, Safety and Seamanship, US | 1 comment

Battery Winter Lay-Up Dos and Donts

What old-fashioned boatyard practice actually increases the overwintering risk to your batteries—and maybe even your boat?

I’m getting ready to have my 38’ cruising sailboat decommissioned and stored for the winter at a local full-service marina. The service manager is telling me that all four of my batteries will have to be removed and stored “for insurance reasons.” This just does not sound right to me, and besides, it adds another $300 to the winter storage bill. What’s the real story?

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Batteries and battery banks are much safer left in place over the winter lay-up period. Just make sure you fully charge them before you de-commission the boat.

In northern climes this has been a tradition for decades: pull all the batteries from customer’s boats and store them in the marina’s “battery room” where they get connected to a constant rate battery charger for the long winter lay-up.
I have contended for years that this practice is far more dangerous than leaving a boat’s batteries in place on board the boat for the winter. So, if in fact an insurance company is still recommending this procedure they should give me a call!

There are at least four risks to removing batteries and storing them with all the other batteries.

Risk #1:  Physical damage to you or your equipment.  Someone will have to carefully maneuver these heavy batteries up and down a ladder without dropping them. Also, consider the risk if in the spring you or someone from the boat yard should accidently reconnect the batteries with the positive and negative cables reversed, which has happened countless times over the years. This is a sure fire way to burn out sensitive electronic equipment at the speed of light!

Risk #2: Centralized explosives. Historically a lot of boatyards would bring all of the batteries to a room, label each one, and connect them to a generally inadequate battery charger that would in turn boil the daylights out of even the most robust of batteries. If you were lucky, someone from the boatyard would be assigned to check the fluid level in the batteries every month or so and top them up as needed. Today of course most batteries are of the sealed variety so the batteries are just boiled until they are toast!

Risk #3: Increased chance of explosion. By moving batteries from all the boats in the marina into one room, we have effectively created one nice, explosive environment. A marina fire would be a complete catastrophe due to the concentration of hydrogen gas and sulfuric acid.

Risk #4 is also the increased chance of explosion, but as a result of a constant connection to an improper battery charger. Even though new batteries are billed as “sealed” they are in fact more accurately referred to as “SVR” or sealed valve regulated, which means that they will actually vent once the internal pressure of the battery reaches about 3 PSI. Once they begin to gas (which they will do if constantly connected to an improper battery charger) they will eventually lose enough electrolyte to get the fluid below the plate grids inside the battery. That considerably enhances the risk of the battery exploding due to an arc between the plates inside the battery.

So, the bottom line here is to fully charge your boat’s batteries before you lay the boat up for the winter, but keep them installed. Yes, batteries will discharge at a rate of anywhere from 2-5% per month just sitting on a shelf. Considering some additional parasitic loads like radio memories and such, you can maybe add another 1 or 2%. But if you start out fully charged, you will only discharge to a 70% or in worst case, 50% state of charge during a normal winter’s rest. No harm done, and no safety concern either.

Ed Sherman

1 Comment

  1. This was a good post. This was my First trip to your blog. Thanks for sharing . I must revisit this blog. I was a truck mechanic for five years. Our repair tip of the week is this: Do not try a exotic repair job by yourself. That can cost you additional money in the end. Thank you ….