alchemysa- yeah, that's the problem with the short answer. Depends on your usage, that's why I rambled so much before that. If you just use the drill once a month, then the battery life is much longer than 4 years. If you use it once or twice a week, then that's the ball park. If I just used it once a month I would not spend the extra money for the lithium versions. In fact, I use mine for something about once a week, and I still stay with the NiCd or nickel metal hydride batteries. As such, you're observation is right on the money.
Pete