I do not trust pep boys, The battery voltage should be at a minimum 12.6 V. and should be higher after a charge. With 12.3 volts you may have a dead cell in the battery. The battery should be load tested before installation back into the car. If the battery passes the load test then the gravity of each battery cell should be checked. You are looking for one cell with a low gravity that says battery is history. More than likely the battery will fail one of these tests. If the battery passes, the charging system of the car can drain the battery giving the symptoms you describe. You will have to start testing again to find out this one. Most of the time it is the battery.
John