These types of displays use power to change the pixels, but almost nothing to retain the existing image, so battery life will be wildly variable depending on how you're using it. Browsing the web with nonstop animations versus reading a book will probably show massive swings in battery life.
It's not e-ink, but it appears to be the same as Sharps "memory" display, which means it continues to show an image even after power is removed. They have extremely low power draw when displaying static pixels
