The NiMH battery in the Insight and Prius are longest lived with many very small discharges and charges (microcycles) - as opposed to deep cycles. In normal driving, you experience hundreds of these in a mile as your foot changes slightly on the accelerator pedal. The battery takes care of these slight changes in demand improving mpg a lot. In order to help longevity, the computer keeps the actual SOC of the battery between ~20 and 80% (someone please correct me if they aren't right)!
Deeper cycling (max to min) several times a day would shorten lifespan dramatically, but in real-life driving that never happens (unless you're drag-racing every day!).
