"The Pro Edition enables the history functionality. Available as an InApp purchase, it adds a range of information, features and charts, as well as the total battery and usage time of your MacBook. Better Battery 2 records data such as capacity, charge cycles, the charge/discharge curve for the last 36 hours as well as the time your MacBook is charging, fully charged and/or used on battery power. The app also records the time that your MacBook is in the optimal range for lithium-ion batteries (40 - 80%). Or it tells you, how much time you've been using the computer and gives recommendations for a daily minimal battery time. You can view all recorded data in easy-to-read charts and reports."
Better Battery 2: Infos & Stats. Monitoring battery health.
agross.at
If I am not mistaken, the app gathers data and presents it in the menu bar. It doesn't drain the battery itself. That is merely a function of the OS that the app is recording.