Charger is showing what mAh the battery has received not it's total capacity. Unless you ran a battery dangerously low you'll never see the full mAh capacity. Charger only knows a battery has been inserted, what volts it's currently at & how many mAh have been used to bring it back to 4.2v. A charger can't tell what the original capacity was, no more than it can know what make/Amp output it is. More expensive chargers can measure internal resistance which would be a clue to authenticity.