I have a Rev A 1.6/80. Just running on battery, the estimated time remaining is normal. About 4:00 with a 97% charge. But when I have it plugged in, it goes really low. About 20-14 minutes. I know I have an almost full charge and the battery isn't shot or anything because I just used it for about 3 hours yesterday without plugging in. Even with the innacurate estimate it still reports the % correctly. The iStat widget reports similar numbers, but not exactly the same. 16 on it, as opposed to 13 in the menu bar.