The cold is good for them, as in they won't degrade as quickly. However, in the cold capacity at that moment is less.
You can use them when frozen, but do NOT charge when frozen.
If put away for longer, best to have them ~45% charged.
Never put them away empty.
Three elements will eventually kill your battery; time, temperature, cycles.
As a DIY user, cycles will probably not be the problem.
Temperature you can exert influence over; store cool and dry.
The effect of time can also be mitigated partly by keeping the charge % around 45%. It will degrade like 3x faster when kept at 100%.
Phone batteries are usually charged too high and discharged too far. This both has detrimental effects on longevity of the battery, but when new this gives it "extra" capacity. So all the low-IQ tech journalists will credit said phone with having good batterylife, even though that will degrade quickly. If you limit top and bottom 5% of a Lithium battery, so say it says "100%" while it's actually 95% and 0% when it's actually 5%, it will live much longer. But then it will show 10% worse runtime in the reviews....
And in the end, the battery will still die. But these days... the failure might be on the circuit board that is supposed to guard over the individual cells....
Different brands have different designs circuit boards. Bosch seems to not do balance charging of the cells, but the circuit is very simple, so unlikely to die.
Makita is said to use 1/2 cells to power the BMS, so even at near-zero power use, that will eventually unbalance the battery and kill it.
Once cells die, you can replace them if you have the knowhow and tools. But that's probably some talk Festool does not approve off.
Beware that some batteries (no idea if applicable to Festool) have the circuitboard designed to 'brick' if it once sees a fault, meaning replacing cells wont result in a workable battery, unless you know how to reset the circuit board. Personally I think such evil should be banned by law, but above all, let's not get into that...
I will be receiving my battery spot welder in a while, so...
