I had to get a Bluetooth HR strap to pair with my Apple Watch, because I couldn't get wrist-based HR readings running in the winter. They simply weren't reliable below 10° C (not minus). Admittedly, that was probably a me-problem, the way my skin reacts to the cold.
Battery-wise, there was only a minor reduction in life as it got colder. By the time it was cold enough for the ambient temperature to really hit the battery, I'd be running with something covering it.
I had to get a Bluetooth HR strap to pair with my Apple Watch, because I couldn't get wrist-based HR readings running in the winter. They simply weren't reliable below 10° C (not minus). Admittedly, that was probably a me-problem, the way my skin reacts to the cold.
Battery-wise, there was only a minor reduction in life as it got colder. By the time it was cold enough for the ambient temperature to really hit the battery, I'd be running with something covering it.