BatteryInfo Pro monitors and shows your battery charge level (percent) as an icon in your status bar with temperature health voltage and time since plugged / unplugged in the notification area. It also has user-configurable alarms logs and widgets.

Free Version Features:
* Automatic time-remaining estimates based on recent usage.
* Several icon sets (including fully configurable green amber red and black icons)
* Small (1x1) and large (4x1) app widgets
* Notification (with status bar icon) is now optional -- can be used as just a desktop widget

Pro Version Features:
* Automatic time-remaining estimates based on recent usage.
* Several icon sets (including fully configurable green amber red and black icons)
* Small (1x1) and large (4x1) app widgets
* Notification (with status bar icon) is now optional -- can be used as just a desktop widget
* Battery logging. You can log the battery state (charge status voltage temperature) and browse the logs on the phone or export to CSV.
* Alarms (full charge above X charge below X temperature above X or health failure)
* Control the notification priority on Android 4.1+ (For example you can set to "minimum" to hide the icon but keep the notification in the tray.)
* Lots of configurability of behavior and appearance.
* The charging indicator (the bolt under the number that indicates when the device is being charged) for the sets that have it is optional in the Pro version.
* Very lightweight (please email me if you think otherwise and I'll help you figure out what's wrong †I promise this app will not drain your battery!)

A one-time purchase now gets you free updates for life on all your Android devices.