How long should an average battery last?

It’s not really a question of how many years or months, although a battery over 2 years old may begin showing some signs of wear-and-tear. The real issue is the number of times you’ve charged your battery. Most batteries will get 200-300 "cycles,"a bit more for NiCad, a bit fewer for NiMH. Less is known about Li-Ion batteries as they haven't had the same scrutiny as the others to date.)