I have to disagree with this. Particularly with the older rechargeable chemistries, like NiCd and NiMH, it is possible to overcharge them. In this sense, it means that the battery is fully charged–that is the chemistry that drives it has been fully reversed–but the charger continues to push the charging current through it. At this point, the current finds other work to do, such as heating the battery even more or electrolyzing the water. This begins to break down the electrolyte, in particular by drying it out. Now, the battery may still “work”, but you’ll almost certainly start noticing a decrease in use time especially after this has happened a few times.
NiCds are more susceptible to this kind of thing, and so-called rapid chargers were the biggest culprits back when the NiCd chemistry was popular. You could get 5-7 years out of a set if you were very rigorous with proper care and feeding of your NiCds, but most people didn’t charge and discharge them properly and the typical lifespan was about 2-3 years. The chargers are smarter now, incorporating ciruitry to detect the battery’s state of charge, and the chemistries are more forgiving of slight abuse, so I think that’s helped things.