On my 4 year-old laptop, the battery discharge pattern is weird. It goes does relatively quickly and steadily down to 6%, then remains at 6% for 1.5 hrs and then very quickly goes down 1%/min.
I had a similar issue with my previous laptop too and never found a proper solution to calibrate the battery properly. If I connect the charger before the charge gets really low, calibration goes haywire.
Any ideas?