The manual indicates that the battery is not replaceable. What happens when the battery no longer holds a charge? How long should the battery last?
The battery in the Clip should provide several years of reliable service. It is a Lithium Polymer unit, and will serve you well as long as you plug in regularly.
If I recall correctly, the battery should get 300-500 full charges (this is full charges; if you only charge 50% at a time, that would take 2 partial charges to get a full charge). And so you can use that to calculate about how long your battery might last.