It was like this for me in U10. Brilliant battery life, even with moderate use I'd get 3 days easily on a single charge. Now, it's extremely erratic. Sometimes it can be good, just how it was before. Other times, I check my phone for the time, and it's gone down 7% in 25 minutes (not an exaggeration).

And my battery is at 95% of original capacity, so it's not that.

I think keeping the browser open does effect it hugely, but I don't understand why now, as it didn't before. Even having MeeCast open (for the tile) drains it more than it used to. A result of the new OOM handling / OS not being allowed to kill processes as it did before?