to clear the watch cache follow the instructions below. Restarting the watch does not clear the cache partition, but it keeps things working smoothly the way auto optimization works with the phone. You should restart that, too, at least once a week. I'm going to warn you here, though, that no amount of cache clearing or optimization will restore a dying battery. My watch4 behaved the same way and the diagnostic still said it was good - until it didn't. There's a certain threshold it may not have crossed yet to come up as not good. If you are not getting even a half a day out of your battery, your battery is bad. It does not pay to replace a watch battery as you will not find any service center willing to do it and if you do, they will not guarantee the water resistance. It will also cost a lot.
The newer watches (7, 8 )have more features and it may be worth considering an upgrade at this point. If you have an LTE watch, you carrier may offer a free one for a new line of service. I did this with mine. I had to pay a 90 day overlap on my old line (but, it was still cheaper than buying a watch - $45 vs. $270). You can also cancel your current watch line 90 days prior to taking any deal.
