Not charging AGM below zero degrees C?


New Member
Hi all.

I have a battery bank of 32 75Ah AGM batteries configured in a 24V system. I'm quite baffled to read in the spec sheet that charging temperature is 0~40°C while discharging temp is -15~50°C.

How sensitive are they really below zero? Can I trickle charge them to keep them topped up or would they be damaged? I have sent an e-mail to the manufacturer but got no reply. Attached is the data sheet.

I do have some other AGM UPS batteries that specify charging down to -15. Seems strange to me that the chemistry would be so different. Just wondering if someone knows something I don't know about this.



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Solar Addict
Good question! My only off-the-cuff WAG:

The ones that are rated for charging under colder temps may be "acid starved". That is, as we all know as you discharge a lead-acid battery, the deeper you discharge, the less acidic the electrolyte - ie more like water than electrolyte. Acid-starved is designed to retain a little bit of acid during deep discharge conditions.

And trying to charge frozen water, rather than electrolyte damages a battery. I suspect the other range of agm's may not be of the acid-starved variety and a major discharge is truly water for the electrolyte for the most part.

My thoughts on trickle-charging top-off are that is *should* be ok, because you are not dealing with a normal deep discharge cycle. Temperature-compensated with a remote probe of course.

But this is just a GUESS on my part. That's a good question to pose to an actual engineer from the manufacturer, and not any sales-droid!


Solar Addict
Everything sub said above.

You can easily insulate and heat a battery system if those temperatures are expected. Often, regular charge and discharge is enough heat to resolve the matter if there's enough insulation, but you need to be careful to provide ventilation to prevent it getting too hot and prevent hydrogen gas buildup from leas acid batteries.


New Member
Thank you for the valuable information! It is in my pipeline to insulate the battery room and in the future there will be a boiler room beneath it so the excess heat from that will probably be enough in wintertime, but that is a few years ahead. I hope I will finish the insulation project before winter, but oh so many other projects and work, so we'll see about that...

Again, thanks!