I got an extended battery from Seidio and I charged it overnight (but not 24 hours). Anyway, long story short, I've let it run down and charge a few times, but this time I decided to let it run down all the way until the phone powered off. Basically I've been using it, continuously, with the battery level indicator at 5% for the past FIVE hours! (Under the phone's About menu in Settings it says the phone has been unplugged from the charger for about 8 hours and 55 minutes.) That includes typing this forum post.
So, is my phone battery meter recalibrating itself? The extended battery is 2600 mAh which is quite a jump over the stock battery. Does this make sense to anyone?