Phone battery always reads 99%

My daughter wore out the charge port on this phone so I replaced the broken charger board. Now the battery always reads 99% all the time. Even if you charge the phone overnight the battery will last all day but it reads 99% all the way up until it turns off on it's own. Also, even if the phone is fully charged, if it is off, the phone won't turn on unless it is plugged in. Does anyone have any idea why this is happening? I double checked my work. This wasn't a problem until I changed the charger port.