I worked at a repair shop 10 years ago and the mechanics always told me not to leave batteries in the cold, especially on cold concrete. It would be nice to know if this is false information. So far it seems the majority of replies say just to unplug and leave in the cold...
Does anybody have proof or a reason why they discharge slower in the cold?
Batteries are little more than a device to permit and control a chemical reaction.
Virtually all chemical reactions slow down as the temperature drops. This is why your battery has less cranking power at "0" than at "32" than at "80" degrees.
A battery charged to 85%--specific gravity of 1.250--won't freeze until -60 degrees F. That's colder than it's ever gotten here, although not by much. A fully-charged battery (1.280) doesn't freeze until NINETY BELOW ZERO. Be aware that we're NOT talking about ******** "wind chill". Wind chill can kiss my azz when it comes to car batteries, and most anything else automotive-related. Fairly important for warm-blooded animals, and your home heating bill, though.
Cold preserves your battery by slowing down the chemical reactions that cause it to lose charge and age. You put food in a refrigerator, the battery is not much different except that instead of slowing down bacteria and mold growth, we're slowing down self-discharge and sulfation.
According to Battery Council International, batteries in storage should
be given a boost or freshening charge when the specific gravity value
drops .040 points. When hydrometer readings are not accessible, open
circuit voltage readings may be used. While in storage, a freshening
charge should be given when the battery voltage drops below
12.4 volts for a 12 volt battery, or 6.2 volts for a 6 volt battery.
Don't get me started on concrete and lead-acid batteries. Either the plastic case is porous so the alkaline concrete can damage or be damaged by the acid in the battery, or the case is intact and there's no problem at all except that the cold concrete will pull heat from the battery and cause it to lose cranking power (which is not the same as causing it to discharge.) I've heard about car batteries and concrete floors since I was in high school. If there's any truth to the problems, I'd love to hear PROOF, not more myths.