Battery drain like that is a pretty good indication that a process is panicking in the background. It's not unusual for this to happen after a bad upgrade, but it's quite unusual to be consistent on a well established installation.
If you are fully rebooting the iPad (turning it full off and back on again) and the drain still persists then I would suggest a full restore, but that is quite a drastic course of action so make sure you prepare (sync and backup). You will be forced to go to 5.0.1, but should still be able to restore your files, settings, etc. from the backup.
IF on the off-chance the battery drain persists after that, the problem is likely something in your backup, so you may need to restore again and set up the iPad as a new device. The downside of that is you will lose your settings and app data, although you can of course get all your apps, media, etc. re-installed via iTunes.