In the morning I got software 6.20 for my 6.45M. As a precaution,
After the first sync over BT and mobile: FREEZE !!
Restart the clock. Now you can see how the battery power decreases 1% in 3 minutes
Reset to defaults, same issue
In my case the watch always freezes after a training, when I saved the run and switch back to the normal display then after a while the watch stops and no button is accessible anymore. A hard reset helps but at the next training it is the same. about the battery drain I got no issues
Are you sure you are doing a hard reset? A soft reset is holding the power button until the device goes off and then pressing again to restart. A hard reset can take a couple of hours by the time you're finished and is completely wiping the device and starting from scratch with all settings www8.garmin.com/.../GUID-1D4D7BAD-1F1A-4EBC-9C74-8D75CCBBF950.html. If this doesn't work, you'll need help from Garmin support to re-install the firmware and if that doesn't work he device should be returned.
You may not have to go as far as doing a hard reset. Others have found the freezing issue fixed by deleting your FIT files. See here support.garmin.com/.../