The batt stats is a file under data, and it attempts to keep a good record of your usage to accurately predict your battery use. It's good to wipe this, if you're able, every two weeks or so. This file can also get messed up if you flash a rom on a non full battery, hence why battery can be worse after flashing a new rom.
Do you know if the stats are specific to an individual battery or are they generalized for any battery that you insert?
I'm under the impression that it's just a log file used by the system to try and help with the battery percentage calculations. Delete it and a new one will be started.