Notebook batteries, not meant to last?

Over the past eight months I have done exactly that experiment, by using two identical notebooks. One has been connected to the mains adapter all the time, being used for approximately eight hours every day, the other has had its battery drained and recharged, usually once a day, but has also been running for eight hours every day. The results are somewhat surprising. The notebook that has been connected to the mains has a flat battery now, basically you get about ten maybe twenty minutes worth of power out of it before the notebook goes into standby. The notebook that has had its battery cycled does not offer the plus four hours of battery life it used to give, but is still good for more than three hours of use.