This happens with every new iOS release, the first few days it looks like the battery life has gotten much worse.
That's not the case.
The first few days after you get a new OS the OS is doing a lot of work during downtime like indexing files, organizing photos, cleaning up ghost files, etc and that work in the background is what's making your battery look weaker.
Give it 2 or 3 days, things will be back to normal.
BJ