i managed to get this deletion task by using locale execute plugin. i typed in !rm file data/system/batterystats.bin, but that still doesnt solve the problem. it resets the time after boot but the usage details still stay there, maybe its something integrated in miui, i dont know.
are you positive that the file is there ? can you see it using root explorer or another root file mgr ?
MIUI is very specific, lotsa files stored in unconventional locations..
then I reckon it's all yours, Pent .. beats me anyhow ^^