iWatch full charge only lasts 6hrs..

Hello alexSE68, Have you checked your Battery Health? On the watch in Settings > Battery Health > Maximum Capacity. If it is below 80% it may be time for a new battery. At the bottom of this page click on Support and Click on Watch under Apple Service options.

As mentioned, check your battery health. You haven’t stated which watch (is it the series 6 listed under your message?) or how long you have had it….so if it’s a watch you have had for a few years and you are the original owner (wasn’t purchased used) and this is something that has started happening as the battery has aged and degraded then it’s very likely it’s time or close to time to replace the battery. Otherwise provide more info if this is a newer watch and your battery life has been like that since the day you purchased it new.