The batteries on the Kindle Keyboard and Kindle Touch are easily replaceable. But honestly, so what? By the time I want or need to change the battery on my Kindle Keyboard, it will be well past time to replace the unit. And the cost of a new eReader will be low enough that it really won't make sense not to go with the newer model.
That being said, I'd probably avoid the Kindle Non-Touch with its glued battery if you're concerned. It is effectively non-replaceable.