The battery percentage display works off the charging history stored in the phone, and when you replace the battery that history is going to be all wrong and show you incorrect values for the charge percentage. First thing to do with a new battery is to calibrate it.
Give that a try, and if it's still not working correctly then we'll see what else we can do to help.
+
+
It is always possible your replacement battery is faulty, but lets see if the calibration helps first before we jump to that conclusion. If you bought it here on iFixit, they have a very good warranty policy for 1 year on replacement batteries.
Hi Davit,
The battery percentage display works off the charging history stored in the phone, and when you replace the battery that history is going to be all wrong and show you incorrect values for the charge percentage. First thing to do with a new battery is to calibrate it.
[[Battery Calibration|Battery Calibration - iFixit|new_window=true]]
Give that a try, and if it's still not working correctly then we'll see what else we can do to help.