3G battery life unchanged after upgrade to 1600 mAh battery

I recently replaced the original iPhone 3G battery with a 1600 mAh battery (part: 616-0366). After the upgrade and after a month of use i don't see an improvement in battery life (vs a 21-month old original 1100 mAh battery). Under medium use, i get the 20% battery remaining pop-up message before i put it on the charger each night. I have tried a hard reset and a restore and reload from backup and still see no noticeable change. Is there anything you need to do after replacing the battery to get the phone to recognize the new battery and take advantage of the higher capacity?