Battstats is a simple utility to track your battery usage.
./battstats start : starts the 'daemon'
./battstats start clean : starts and cleans the log file
./battstats start 2 : starts with 2 minutes (or whetever it is set) measurement interval
./battstats start clean 2 : same as before but it cleans log
./battstats stop : obvious
./battstats : prints information about battery percentage and time remaining
./battstats help : prints this help screen
battstats.log contains information about computer state (charging or discharging), time on battery and relative battery percentage.