BatteryInfo-Pro

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.

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 configuration of behaviour 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.