Battery life in freezing winters

TimC

WI/UP Border
After four winters my camper batteries are going strong. I have eight 18aHr AGM batteries and they are always on active charge 365 days per year. I don't take them out of the camper in the winter and the camper is unheated and sitting outdoors.

I occasionally read that batteries should not be kept in a freezing environment for long. Why are my batteries holding up so well if that is the case? Are these statements just about batteries not kept on a charger?
 

TimC

WI/UP Border
I am asking because I was recently looking at a home backup system (gave up on that idea for now). With that system I was hoping to keep the batteries in an underground bunker sort of thing so they could be near the solar array. The thought was the wiring sizes would be much smaller running 115v across the yard vs 12 or 24 volt.

I was advised to never do that.
 

45North

Let it shine!
After four winters my camper batteries are going strong. I have eight 18aHr AGM batteries and they are always on active charge 365 days per year. I don't take them out of the camper in the winter and the camper is unheated and sitting outdoors.

I occasionally read that batteries should not be kept in a freezing environment for long. Why are my batteries holding up so well if that is the case? Are these statements just about batteries not kept on a charger?
Where are you and how cold are the winters where you are?
 

TimC

WI/UP Border
WI/MI border (45.7). Average temp in January/Feb is probably 25-30 degrees. Occasionally below zero for six or eight days. So... cold. If your handle is what I think it is you are probably familiar with that kind of cold.

In garage might be ten degrees warmer on average.
 

MichaelK

Solar Addict
As long as lead-acid batteries are fully charged, they won't freeze till the temperature drops to ~ -40F. The sulfanization reaction is accelerated by warmer temperatures, so they sulfanate more slowly when cold. Storing lead-acid batteries cold is good for them, assuming they stay fully charged, which seems to be what you are saying.

I think the worry is batteries that sit for very long periods of time unattended slowly discharge, so by the time winter comes around, the state of charge is not high enough to keep them from freezing.
 
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