Since the UA-5 was powered by an external battery, I only ran the iBook from it's internal battery. It usually lasts me 4+ hours, so I never had a problem getting a whole show. Did a couple of DMB shows like this, around 3 hours each - no battery problems.
Now I have a Valence NCharge, which gives me around 10 hours of use - but since I run the 410 powered from the firewire bus I get about half that for recording.