Bought to replace my Dell Inspiron 1545's battery, whose life after two years had decreased from 2 hours to 10 minutes.
Replacing the battery is easy: turn everything off, pull out the plug, turn the laptop upside down, and toggle the little switch to "unlock" the battery before sliding it out. The new battery then just slides in place, clicking in like a car seatbelt.
Being a 9-cell battery, it's bigger than the original 6-cell one, and so bulges out of the back, but in a way that has obviously been carefully designed. I now get an unprecedented 4-5 hours on a charge (with the screen at a moderate brightness). So far, just as good as the far more expensive "official" Dell batteries.
One oddity: Windows 7 would sometimes "warn" me that my battery was low, displaying a little exclamation mark, but at the same time showing (truthfully) that I had 90% and several hours left. Possibly a side-effect of this not being an official battery, but not intrusive.