Hi guys,
I just wanted to chime in. Same problem here - Apple Watch Series 3 + LTE will not charge above 95-98% even overnight. I bought it on day one. Every few days, it stops charging fully, stopping at the mentioned percentage.
The short term fix was just to hard-restart it (by holding both hardware buttons until it shut off and then starting it again). Then it will fully charge again and for a few days.
I contacted Apple Support and the first time they wanted me to factory reset. I eventually got around to contacting them again this morning (obviously the reset didn't fix it, started happening a few days later). They are sending me a box that they said should arrive within a few days and they are going to repair it. Unfortunately, they made me factory reset it before they started the repair process, so I'm out of my watch until the box arrives and its repaired. Was hoping to get a few more days out of it
They said just to send the watch face, and hold onto the band and all accessories; I'll update when I get it back to let you guys know if it was repaired or if they send me a new one.