After some testing this is reproducible. Given the following conditions:
- The watch is away from the iphone
- Cellular and mobile data are on
- Listening to music
- Activity tracking and heart rate monitor are running
The watch invariable dies after about 30-40 minutes usage - and by this i mean it just resets itself.
Attempting to start the watch and initially it hangs with the apple logo before shutting down. After a fairly long time (30m-1h) the watch does start up. Sometimes the battery will show plenty of charge left e.g. 60%+
On the other hand, running the activity monitor and music whilst the phone is close by, and with mobile data turned off, results in the expected slow battery discharge.
My conclusion following these tests and observations is that all the running processes above coupled with the watch being away from the phone, requires more juice than the battery can cope with delivering, and it either overheats or discharges at a rate that it can't cope with, resulting in a shut down. The battery seems to remain in this strained state for some time, resulting in the watch not starting up initially. Eventually the battery recovers enough and the watch is able to start up and function as normal.
It's not particularly impressive, and does make me think that apple watch is not the perfect companion for sports users. My use case was to be away for 2h (from full charge), with cellular, track my sports activities and perhaps listen to a bit music. It has failed to deliver in this case unfortunately.
