I've had no issues with battery drain using the new OS. It's just about the same as the old one. I've heard that it helps to have a magnetic holster... but haven't gotten around to that yet. And yes, make sure to actually "Close" or "Exit" programs rather than just push the red x button.
Upgraded to .148 and have had no issues on TMobile with a 9530 on GSM mode with heavy usage. Kicked me down to 70% after being on the phone for 5 hours, heavy emails and texting yesterday! I must say prior to yesterday I would have been probably been a little lower (partly due to 3rd party apps affecting me), so I am pleased and will look at grabbing an even bigger battery from seidio!
