For a LiIon battery, i recommend whenever you are at your desk working on the power from the wall, that you simply remove the battery. The steady trickle charge from running on a full battery with the A/C adapter connected will reduce charge over time.

With my first battery within 8 months of keeping it plugged in the whole time with the battery in I went from ~3 hours to ~1 of battery power. Now I just remove the battery when I'm at my desk.

Be sure to put the battery in before unplugging the computer!