rechargibg batteries below 0°C

Other Hardware Motors, Mechanics, Power and CNC
1

Hello everyone, I'm starting a project that includes the installation of small stations that measure the melting of the snow on a snowfield, and we need to understand how to go about the batteries, also to be connected to a solar panel.
Last year those had done their job for about three months:

Function below zero, but I do not think you recharge below zero, and are quite expensive.

I read instead that the best solution for cold climates are lead-acid batteries, which can also recharge below zero:

So I found on Amazon this model:

http://ultracell.net/datasheets/UL4.5-6.pdf

I read the documentation:

Discharge: -15 ~ 50 ° C (5 ~ 122 ° F)
Charge: 0 ~ 40 ° C (5 ~ 104 ° F)
Storage: -15 ~ 40 ° C (5 ~ 104 ° F)

But 5 ° F are 0 ° C, are always 15 ° C like in the other two cases, and so what is the error?

Any other suggestion is very well accepted, thank you!
I imagine that the alternative to heat the battery with a little resistance is not very feasible because of absorption, but I could be wrong.

2

Vehicle batteries have to cope with this all the time, I suspect the datasheet is being conservative
to prolong service life. lead-acid cells cope with lower temperatures when fully charged as the
electrolytic strength is greater and this depresses the freezing point more.