A bloody long time! I spent the documenting a maintenance activity at Yallourn Power Station (Australia, Victoria), which involved, amongst other things, three hours in a helicopter photographing another helicopter and I took 1428 photos, including some video, and when I'd finished, the battery indicator was still showing two thirds full. I did very little chimping and turned off the camera when not taking shots. And on a side note, the IBIS and 4/3 lenses proved their weight in gold. I'll post more on the assignment once I've gone through the photos and videos, and have approval to post results.