What is the battery health of your 3?! I upgraded from a 4 that needed to be charged twice a day after battery dipped below 80, which made it not very useful for me.
So now I have it as a backup and it gets turned on like once a week when I need a watch but my 7 is charging! (If you go this route, make sure to charge old watch to at least 60% and then turn OFF from the settings menu til you need it next time).