Today I took apart my N9 and replaced the battery with a new one I bought online. Unfortunately the new battery was dead upon connecting it (the tiny notification LED didn't light up when plugging in the battery), but I was able to get it to charge by plugging the phone into a DC outlet. Now when I turn on the phone, the battery always starts at 100%. Phone "drains" to 80%, reboot, shows 100% on reboot. Does anyone know how I can fix this so the correct battery percentage is displayed?

EDIT: Also, when I try to charge the phone I always get an error that something went wrong with the charger.