A year ago I started using a script that takes a snapshot of a MacBooks' battery health every minute. It captures weather or not you are currently charging, how much charge you it has, and what the estimated current max capacity is.
Now that I've built up a year of data, Piet van Dongen recently contributed some coding to graph that log, so I wanted to put this up for others to share.
This is 365 days of battery on a 2012 MacBook Air. You can match some of this data up to my Annual Reports.