In my case, during the first month I got around 50% every 7 days.
But a couple of weeks ago the battery suddenly started lasting only 3-4 days. I turned off AOD as recommended above, but the same thing kept happening for two weeks.
I restarted the watch and it seems that did the trick: things returned to normal (with AOD off) and now it’s at 85% after 5 days. Just my two cents, in case anyone finds it useful.