If you've replaced your battery it's possible the design capacity is different from the original. Usually the design capacity will be written on the battery so please take a look to see if the number is the same as what our calibration process found. If it's not, you can manually change the design capacity by going to the charging tab > battery capacity estimate > change design capacity.
If you want to reset your stats: you can go to phone settings > apps > AccuBattery > clear data. Then the next time you open the app with the new battery in, just re-run the tutorial + calibration and it should start tracking your new battery. We don't have support for simultaneous use of multiple batteries yet but that could be an interesting option for the future.