For the battery, seems to me there are two engineering approaches, specification and characterization.
For the specified battery 4400mAh https://www.adafruit.com/product/354
which has a listed data sheet from the manufacturer – https://cdn-shop.adafruit.com/product-files/354/C449_-_ICR18650_4400mAh_3.7V_with_PCM_20140728_APPROVED_8.18.pdf
it has a defined “Operating Temperature” of Charge: 0-45C, and Discharge -20 – 60C.
If you go outside those parameters, for too long (!) – some may still operate – but now its characterization as to how many will operate.
Of course manufacturers do characterization upfront on their products, to be able to come up with a specification they stand by across all that product range.