At load, I suspect the Intel based E480/580 may experience shorter battery life as it needs to supply the dedicated GPU with additional power.
erm... depends on what kind of load you are talking about. CPU load? Games? Videos Transcoding?
If doing heavy gaming or video transcoding, I doubt anybody will expect more than 2.5 hours on either the e485 amd or e480 intel with graphics, which makes the discussion on battery life irrelevant. An extra 20 mins of battery is not going to bring much value. The dedicated graphics don't kick in unless the IGP cannot handle.