When this happens to me, I look at a couple of things. First, I peek at GSam Battery Monitor to see if there's any processes consuming an unusually high amount of CPU time. Lately, on my Verizon S3 running VRBMB1, I can see SDM_something_or_other causing a high number of partial wakelocks and chewing up CPU time (and thus battery). I *think* this process has something to do with OTA updates, which I keep deferring to stay on MB1.
The second thing I check is "System Settings" -> "Developer Options" -> "Show CPU usage". This can help identify a runaway process. I'll see something called "gsiff_daemon" occassionally here in the red.
If SDM is the culprit, I'll clear the SDM app's data, force stop it and reboot the phone. If gsiff_daemon is causing me grief, I'll just reboot the phone. These actions successfully stop these processes from hogging CPU and eating my battery.