Cycling MacBook Pros??

Apple recommends that you calibrate (give it a full cycle) every month or two. 20 cycles in five weeks is probably about normal. A very rough guide is that a battery should give 300-500 cycles before it drops below 50% capacity, but your mileage may vary...a lot.

Just do the calibration thing every month or two and don't worry about it...the battery will die when the battery dies. The software does a very good job of monitoring charge state and preventing overcharging and repeated short charge cycles.