[HarryT]

In what way does that constitute a rental agreement? The key difference between renting and purchase is that when you rent something you don't own it. The fact that an eInk reader has a limited lifespan does not alter the fact that you own it, and hence in no way whatsoever are you renting it.

You can replace the battery in pretty much all devices, should you wish to do so. Given, though, the way that prices drop and technology improves, whether you'd wish to do so after the 5 years or so that a lithium battery will last on average is open to question.