Upon installing 5.0.1 it will reset the iPad automatically.try a soft reset - press home button and lock button until ipad turns off (don't use the slider)
How many apps are there running in the background? It is always a good idea to close all apps and did you reset your device after the upgrade? I always keep my brightness to about 25percent.Update 5.0.1... Still ticking down despite being locked. Lost 10% in 2 hours after no used other than reading this forum....