Battery Health is a laptop battery statistics tracking and analysis application. It can reside either in the menu bar, in which case the application appears only when the menu icon is clicked, or in the dock, in which case it behaves like a regular application.
It displays the following information about your laptop battery: the current charge, the current and original maximum charge, the battery time remaining based on activity (current usage, Internet browsing, music, movies, or standby), the temperature, the age in years and cycles, and the power usage in watts and milli-ampere-hours, which is additionally represented over time in graph form. All this information is well and good if you know what's what, but Battery Health has you covered even if you don't. Question marks icons by each section elucidate the statistics when clicked, in a way that almost any user could understand.
Sam's Protip: FIPLAB beat me to it! Click the Tips button for ten things you should know about optimizing laptop battery usage.