yesterday my mbpr 13" battery capacity suddenly dropped from 6300 to 5990 . i unplugged the charger for 1 minute and plug again,it jump back to 6250, once the power plug remove few sec, it drop to 59xx again, if i do the same step above it will back to 62xx again. and this situation keep repeating. is this behaviour normal ? because i nv seen this happen on mine before.