I'm adding to this thread because of a variation on the battery drain issue. In this case, I suddenly found that the battery would be empty after about 3 days or so. "Have you tried turning it off an on again?" Yes, and it made no difference.
When I finally looked with adb, and used the pastlog command from the shell, I found that the pastlog was full of messages like this, one per about 10 seconds:
log_radio opening data channel device - /dev/ttyUSB0. retrying...
Some googling taught me that this is from the "RIL", radio interface library. This url tells about that: http://afewe.wordpress.com/android-a...il-in-android/
I was thinking about drastic things like killing the RIL daemon, but it turned out that the poor thing was probably confused about whether the WiFi (or phone?!) was on or not: it was trying to open the device to the modem emulation.
Simply turning the WiFi on and off again made problem disappear.
Let's hope it stays unconfused for a while, since I don't know how it got into that state.