Lithium battery usually can be charged 300-500 cycles. It won't abruptly stop working. Like a laptop battery, it will gradually keep less and less charges (the runtime will be shortened).
They can be charged at any level. Modern lithium batteries do not have memory effect. We do recommend taking it off the charger once the battery is full.
We have not tested it in extreme weather. Generally speaking, Li-ion batteries are recommended to be charged between 32°F to 113°F and used between –4°F to 140°F.
Generally speaking for Li-ion battery
Charging temperature --> 32°F to 113°F
Discharging/Use temperature --> –4°F to 140°F
At lower temperature, the worst can happen is the battery temporarily loses 10-20% capacity.
(Our low temperature 18650 batteries (NL1829LTP etc) can operate at –40°F)