I may have found an answer to my question. My battery life is back over 24 hours. Investigation suggested that it was syncing-related. I tried the following two things (after other failed attempts) based on the weak evidence I had:
Set my phone to always keep wi-fi on during sleep (under Wi-Fi, under Advanced in the menu). I have weak cellular coverage in my house, so falling back to cellular isn't necessarily better for battery.
Disable Currents from syncing. It is a heavy abuser, and I don't use it.