Despite being a B1, the battery life on my 17 PM is pretty good so far. I haven't encountered any issues so far with the apps I use, and stability is great. For my Ultra 3, battery life is on par with 26.5, and 27 also fixed an annoying bug where the "clear all" notification button wouldn't work. On 26 and 26.5, sometimes I had to get rid of the notification screen and then swipe down again for the clear button to work.
So far, 27 B1 has fixed that annoying watch issue. For a B1, it's a really good start.