The tests were presumable done on equal footing - 50% screen brightness, full battery charge, with both phones connected to LG's U+ network. The results are as follows - 15.8 consecutive hours of talk on the Optimus G, compared to 9.5 hours on the Galaxy S III. The official specs of both phones are 15 hours of talk time in 3G mode for the G, and 11.5 hours for the S III, though.
Optimus G also recorded and played videos for 3.8 hours and 7.9 hours, respectively, whereas the Galaxy S III managed 2.8 hours recording and 7.3 of video playback.
The reason for this frugality was demonstrated for reporters playing PSY's "Gangnam Style" video, and while playing a 1.8 GB video game - in both cases the Optimus G showed lower power consumption compared to the Galaxy S III. Overall, the test results, while not independent, aim to confirm that the Optimus G, despite all the power stuffed into it, is not going to be less frugal than Samsung's most popular Android handset, which has the same battery capacity.