We also have a KindleBoards Alternate Pick of the Day: Battery HD
This nicely done app lets you know "How long can I?" for various items such as Music Playback, Video Playback, Internet Browsing, Online Radio and LED flashlight. It also, of course, tells you how much battery you have left at the moment, how long before you'll need to charge given the current level of use, and the battery temperature. It does provide data for actions that aren't available on the Fire. There is a tiny ad at the bottom of the screen. If this bothers you or you want to support the developer, Battery HD Pro is available for $2.00.