[Mike L]

The amount of battery power that the Kindle uses while at rest is absolutely negligible. The only time it really uses any power is when you are interacting with it, that is, turning pages, using the keyboard, moving the "cursor", and so on. And even then the drain on the battery is small.

Turning it off might or might not be a good idea, but it certainly won't save any electricity.

Whispernet is another matter. If you want to save energy and conserve your battery, keep Whispernet switched off except when you are actually using it.