I went for a run in 15F weather with about 75% battery charge and it shut off less than one hour into my run--only to restart and say that it still had 54% battery charge after it warmed back up
The only complaint I've had with my 630 since I bought it when it debuted is that in cold temps the watch will shut off unexpectedly.
after a while i noticed that it only occurs (even before showing the "battery low" - alert) when the watch takes an "autolap" AND vibration is turned on
Interesting point. I typically notice the same thing, but had always assumed that the cold causes the watch to perceive that the battery is lower than it actually is...