Mine was killing the batteries in under a week also. I checked the status in the menu
Settings>Remotes and Devices>Remotes>Voice Remote>About
The "about remote" menu shows the battery level and the remote's firmware version, and at the time my RC399 remote's firmware was on version rtn.4080 .
I contacted support on Jan28, 2021 , explained my situation in detail. Batteries would last less than a week before.
Now my remote's firmware version is now rtn.4086 (they must have updated it?) and battery level is at 62% after 2 weeks . My battery drain issue is much better. Still not great but a huge improvement that I can live with.