I went out cycling this evening and it suddenly shut down. on turning back on, every time I tried to resume the activity it turned itself off and on again. I have now done a hard reset [turn off then turn on while holding the down button] and it seems to record an activity, but it won't synch via garmin express and there is no synch option on the watch to synch it by bluetooth.
I can see 4 activities on the watch through file manager on the PC and I can see the 4 activities in history on the watch.
another hard reset and it turns itself off when stopping an activity.
another hard reset start and stop an activity and I can see 5 activities but it won't synch via garmin express. I have managed to synch a workout to the watch from garmin connect via express, so it isn't completely disconnected but the workout won't synch after it has been saved. there is still no synch option on the watch.
from fully charged, it lasted 3hrs 15min till it got to about 33% while recording a 'ride' [on my windowsill] with the backlight on. then I pressed a button and it rebooted. plugged it in and it recovered.