This. I'm testing a new Oasis 2, at first I was stunned by how fast the battery drained. Then I read more here on MR and realized 2 things:

1. Indexing a bunch of new books you load onto a Kindle takes a while and drains battery fast. Mine was still indexing.

2. I needed to turn on airplane mode, which disables: 3G cellular (if you have that), Wifi, and Bluetooth.

Battery now is right where I'd expect. It dropped 1% over night in sleep mode. When I read with the light set at "10", and it only drops 3 to 4 % points per hour. Of course mine's new, so I don't know how this battery will break in and perform over time.