Yes mine was doing this suddenly too. I worked out it was not connecting via Bluetooth any more so constantly polling was killing the battery.
Solution: remove the device from your garmin connect app, again from the website (yes, this is held separately to the app!) and also on garmin express.
Then restart the watch.
Go to garmin express and reconnect the device.
Once you open the app you will be able to re pair the device via Bluetooth.
