The 10.3 update killed my watch.

Not something I have experienced. Are you sure it’s the update that’s the issue and not a problem with the charger being used? Have you tried charging with a different one to see if it works? Or are you saying the battery drained fast overnight while you were wearing it? If so, you can try the usual suggestions…restart the watch. Reset. Unpair and then pair it again. Restore. All hassles but may help. If none of that works contact Apple Support for further assistance. It may be something another update needs to address though.

This just happened to me a couple of days ago. Watch was working perfectly and I put it on charge while getting ready for bed and it did an update. As soon as it finished charging it was dead. Like it keeps short circuiting and can’t load the new software. I’ve tried different chargers and everything and still nothing. Called apple and even though it’s only just a year old and just out of warranty I am going to have to pay to get it fixed. Totally unfair and unjust giving that their software is what caused it. It is a series 8 model too so not like it’s really old. I don’t have the money to buy a new one. The more I am reading the more I am seeing this is a problem for Apple Watches.