Me too! My battery level has completely plummeted due to this update. I've gone through every setting on my phone and turned off lots of features as well as updating all my apps in hopes that it would help, but nothing has.
Previous to the update I had excellent battery life; I'm using a 2nd Gen SE and although it's an older model the phone itself was nearly new. Now since the update I'm being told that my battery needs replaced.
Supposedly after any update there are background actions occurring that can affect battery life for awhile, but after a month nothing has gotten better.
Then of course they released 17.1.2, which only addressed some security issues, and next month another big update will be released, so who's to say how long we'll have to wait to see if it helps. Here's hoping that it finally does something to fix this battery drain, but I'm not holding my breath.
Apple has a history of intentionally destroying battery life in an attempt to force users to upgrade, they've even been sued for it by entire countries and found to be liable.
But apparently that hasn't stopped them from ingaging in bad business practices that is only going to result in a lack of trust from their customers.