Well, our models are different then.
My ProBook 4530s (B0W80ES) (Core i5 2450M 2500 Mhz/15.6"/1366x768/4096Mb/320Gb), your quiet fan DSDT patch is installed.
Just browsing - 1,5 hour.
Running apps, iTunes playback, iWork, iPhoto - 1 hour or less.
Video playback - 40-50 minutes.
Can not...