I have this exact same problem. Called Resound and they had me disconnect and reconnect the hearing aids. Did that and it didn’t fix the problem. They referred me to Apple Accessibility support.
Note - prior to this I had deleted the resound app and removed the aids from accessibility and the Watch kept its charge like normal - around 30 hours. Reconnect the aids and the Resound app - maybe 8 hours on the Watch.
Called Apple Accessibility Support and they said that the Watch isn’t connected to the hearing aids so that isn’t the problem.
I deleted the Resound app and removed the aids from accessibility - 28 hours on the charge. Reloaded the Resound App, 8 hours.
Resound support made it sound like this was a fairly common issue.