Battery Guardian

Battery Guardian helps you keep your Mac battery healthy. A healthy battery is one that is regularly depleted and charged all the way back up.
Battery Guardian offers an easy way to remember to deplete your battery.

30 days after your battery was last depleted, Battery Guardian will remind you. Battery Guardian puts a small heart in the top-right of the screen. When your battery needs depleting, the heart will turn red.
Battery Guardian can also add an event to your calendar to remind you. This can be particularly useful because the calendar can be shared across all your devices. A quick look at your calendar from any device, will let you know if your laptop battery is due for attention.