Winter Battery Storage - SailNet Community
LinkBack Thread Tools
post #1 of 1 Old 01-16-2002 Thread Starter
Contributing Authors
Join Date: Jan 2000
Posts: 266
Thanks: 0
Thanked 12 Times in 8 Posts
Rep Power: 21
Winter Battery Storage

I am wet-storing my boat for winter, but I am concerned that the batteries will freeze during the few weeks when the temperature gets in the low teens. Do you have any suggestions on how to keep the bilge pump supplied with power?

Tom Wood responds:
A few weeks in the lower teens? Not to worry. Here are the facts:

Acid will freeze, of course, as will water. The temperature at which the electrolyte in a fully charged battery freezes is about 75 degrees below zero Fahrenheit—which is why cars still start in the arctic in winter. On the other hand, the electrolyte in a mostly discharged battery is close to the specific gravity of water, and it freezes just below 30 degrees. So the first imperative is to get the battery fully charged and to keep it that way for the duration of the winter.

The main threat to the health of a battery comes from it standing idle. When batteries are used frequently, being discharged and fully recharged on a daily basis like they would be in the family automobile, even a cheap one will last a long time. This is because the chemical process "stirs" the electrolyte and cleanses the lead plates. When batteries sit for long periods of time between use, some of the sulfuric acid forms sulfate crystals that coats the lead plates. This coating gradually gets thicker, interfering with the chemical process between the lead and the acid. Some of this cooking can be "blown off" the plates by an equalization process—applying an unusually high voltage to the battery for six or eight hours. But the best way to take care of it is to prevent it by keeping the battery charged.

All batteries lose power over time and need to be recharged, even if they aren't used. The rate of this "self discharge" is about 1/100 of a volt per day for wet batteries, less for AGM or gel batteries. This is about 25 percent of battery capacity per month, so it's a good idea to recharge idle batteries every two weeks or so.

If your marina does not have electricity over the winter to operate your battery charger, I would recommend that you invest in a small solar panel to do this job. A charge rate of about two percent of the battery capacity is a good rule of thumb because this amount would be incapable of overcharging the battery and would not require the addition of a voltage regulator. This translates into roughly 25 watts of solar panel for every 100 amp-hours of battery capacity—a little more for northern boats in the winter because the sunlight is weak, there are many cloudy days, and daylight hours are short.

Tom Wood is offline  
Closed Thread

Quick Reply

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Forum Replies Last Post
Battery charger for winter storage? pegasus1457 Electrical Systems 22 06-25-2010 07:41 AM
Battery life? Winter storage? saltypat Gear & Maintenance 12 12-03-2008 11:57 PM
water storage vs. land storage during winter apkaplan General Discussion (sailing related) 1 10-24-2007 04:50 PM
Battery Winter Storage bjoc2314 Gear & Maintenance 9 11-14-2002 03:57 PM
Winter Storage RPerreca General Discussion (sailing related) 7 06-15-2001 05:34 AM

Posting Rules  
You may not post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is Off
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome