The batteries are identical in size. With regards to battery life:
Test 1: Playing a movie (stored on hard disk, not DVD) with the Optimus settings on amber (GPU turned on): 2 hours 25 minutes
Test 2: Playing a movie (stored on hard disk, not DVD) with the Optimus settings on green (GPU turned off): 3 hours 30 minutes
You should expect a 62.16WH battery to last 27% longer than a 48.84WH battery.