Originally Posted by Maine Sail
A fully charge battery will not freeze until it's colder than -70F. I was born in Alaska and my folks were there for years, in Fairbanks, and they only had flooded batteries back then. Freezing batteries was not an issue but tires that went flop, flop and cracked steering wheels were when it hit -50 - -60F.. The batteries survived just fine but had less cranking amps so many cars had bigger batteries then they shipped with.
Keep in mind that in warmer temps the rate of self discharge & the chemical reaction rate/sulfation accelerates so keeping the batteries "warm" can have less benefit to storing them in a cooler location at your house. In cold temps sulfation is virtually non-existent and this is why ours have always been stored on-board every winter. Many boat yards require batteries to be "disconnected" from the vessel, if left on-board, as they should. They allow top up charging while you are there but generally disallow batteries to be left on-charge..
If leaving them on-board they need to be 100% disconnected and charged them to full...
Absolutely right. Batteries don't freeze if kept charged. They do, however, lose charge more quickly when it's cold and I want to cover the boat and leave it all winter without having to check it on a regular basis. I don't plan on seeing the battery compartment until spring. The issue always in the back of my mind is that if there were ever a fire in the boatyard, no one could point the finger at me for a battery short being the cause. I also remove all signaling devices because if there were a fire, I would not want the guys in the FD having to deal with SOLAS flares going off.
I keep the batteries in my garage, where it is usually 40 degrees or so and occasionally put on a charge to keep them up to voltage. They are heavy sobs and I always dread disconnecting all the wires, ANL fuses, etc. and then getting them down the ladder and into the car.