To add to the battery calibration, try running
HWMonitor. It should give you the wear level as a percentage.
I'm not sure if all of the Dell batteries with built-in power gauges do this (the one on my Inspiron E1705 does), but if yours has the gauge, try holding the button for 3 seconds. A quick press tells you the current charge, while holding it for a few seconds should tell you the wear level (IIRC, 5 lights=40% wear/recommended replacement).