On: The De-evolution of My Laptop Battery

[Scaevolus]

RRDTool is great for storing these sorts of time-series archives, and it will generate pretty graphs as well. You could cobble together an app starting from these StackOverflow postings:

Task Scheduling: http://stackoverflow.com/a/2725908

RRD interface: https://pypi.python.org/pypi/PyRRD

Battery reading: http://stackoverflow.com/a/6156606