Winter Storage of Batteries

Can anyone explain what the dangers or risks are of leaving my boat's ten 12V batteries onboard during the winter?

I had hoped to be able to store my "new" 1984 MT 40 Sundeck Trawler in an inside heated facility this winter, but the two marinas on the Hudson River, just south of Albany, NY, offer only inside unheated or outside winter storage.

Since I live in Chicago, there's no practical way for me to remove them, bring them home with me, and keep them in my garage or basement over the winter.

I don't know if either of the two marinas could remove and store them in an inside heated area for me either. Nor do I know if there's any way for me to run an electric extension cord to the boat in their outside storage yard to power a trickle charger or small low-powered heater during the winter.

Thanks.

No danger just ensure they are fully charged and disconnected before leaving the boat

L

Lead acid batteries that are fully charged or close to fully charged won’t freeze. But dead or nearly dead batteries will.

So disconnect the batteries at the terminals so slight ongoing loads like a CO detector won’t run them down. But FLA batteries can self discharge, so to be sure, it would be good to hook up an external charger 2-3 times during the winter for a few hours.

I didn’t bother with charging in the Ct, LI Sound climate, but poor batteries can self discharge faster, so be forewarned.

AGMs self discharge at a very low rate, so you don’t have to do this with that type.

David

Yep, get them fully charged, disconnect ANY possible drains, and they will be fine. Also second that it is good to top up the charge a couple times during the winter.

If you do that and a battery is dead in the spring, it was in crappy shape anyway.

The boatyards are experts at these issues, talk to them directly about what their SOP is and if they offer the service of charging now and then. Inside storage has a lot of advantages in that you don't have to shrink wrap the boat.

The first year we owned Stella and shrink-wrapped her for the winter of 2014, I thought I’d disconnected all loads but missed one parasitic draw. Our 8-D house bank froze and died during the Polar Vortex when temps hit below zero in Delaware City. Every year since, I’ve fully charged the bank, disconnected every cable and had almost full voltage in the spring. We have AGMs and I only charged once over the winter to be on the safe side. Probably wasn’t necessary.

A lead-acid battery will freeze, even fully charged, but it takes about -80F to freeze it.

If you use a glass hydrometer to test SOC and the specific gravity of your battery, it will show the freezing temp of the water in the acid.

Also, the longer a battery sits, the more likely you'll get battery stratification, which is the separation of the water and sulfuric acid, with the acid on the bottom. Once this happens, the freezing temperature becomes 32F. I've seen batteries that froze after stratification, and they pop the cap off the top since the acid is still liquid but when the water froze, it expanded against the upper sides and top.

If you're storing batteries for 4+ months, unhooking them will help protect against the parasitic drain, but adding a solar maintenance charger will be the best protection. Lead-acid batteries do self-discharge at about 4% capacity per week.