After the last OS26 developer beta update the watch series 6 battery drains fast, in less than two hours life. I visited Apple Store , they said the battery was dead so I had to buy new watch series 10 The same issue happened in the new watch, the battery meter shows 50% after 1 hour Right now I’ve downgraded my update version to beta 11 until I can find a solution
watchOS 26 cause Battery drain fast
My Battery drain is not as bad as OP but my brand new series 10 watch is definitely battery draining noticeably faster than before I updated from 18.5.
Temporarily I installed OS11 beta on my watch series 10 OS26 developer beta in my iPhone 16 pro max It’s working fine its obvious the problem is in watch OS26 beta