The computer was an IBM ThinkPad T41, the accu a 9-cell extended accumulator with originally 78 Wh, slightly used (33 cycles) and somewhat older (manufactured end of 2004, tested here at 2009-11-21).
Accu runtime of that setup: 5h 39min. At screen brightness level 5 of 7, screen always on, Windows running, but no applications running.
After the 5h 39min it showed “3% remaining capacity” (probably just when the voltage went below 10.8V nominal voltage, which you can see in the ThinkVantage accu info dialog) and immediately went into Windows hibernate. Then, when booting into BIOS, it run 2 minutes until the “heavy” beep alarm rang, and another 30s before it went to suspend-to-RAM. Then it was only able to start / resume with the AC adaptor plugged into, and immediately went into suspend-to-RAM again when plugging it out. It remained in suspend-to-RAM (without AC adaptor) for something between 15 and 24 hours (so probably around 20 hours) when it finally switched totally off.