I've had my aluminum Nike S3 for about 8 days now and have had two instances where the watch will turn off without warning. I haven't had it happen while using an app on the watch, but both times I tried to check the time and noticed the watch was off. The watch had around 70-80% battery during both instances. When I power the watch back on it seems to work fine. Is anyone else experiencing similar issues or have any idea what may be causing this?