I had the same problem repeatedly that many users reported. Nokia 3 did not charge fully but (obviously) stopped at 60 or 70 %.
After much googling and doing same experiments I found the following solution which worked for me.
Step 1: Let the Nokia battery drain until Android automatically shuts down.
(Beware: battery is not yet fully discharged).
Step 2: Connect original Nokia charger and boot into Recovery Mode (hold Vol+ and On-Button for 30 sec).
Step 3: Disconnect charger (important), wipe cache partition, and wait in this mode for 2-3 hours until Nokia
ultimatly shuts down. Now the battery is completely discharged.
Step 4: Connect charger again, but do not yet start Android ( ! ), let battery charge and wait for 3-4 hours.
Step 5: When full, start Android the normal way (Hurray) !
Explanation: The charging problem occurs because Nokia has a smart battery - it detects overheating in charging
and protects itself. Thats why in such a case the percentage shows only 60% or 70% (although truely it is charged to 100%).
Draining battery in Android mode does not help because Android shuts down long before the battery truely is empty.
In Recovery Mode it drains completely and the battery statistics is now resetted (wipe cache partition).
This procedure is NOT healthy to the LI-ION battery and should not repeated regularly.
Prevention: The irritating battery percentage occurs when Nokia 3 is charged under warm conditions
(eg near radiator or when some heavy bachground processes run or with a charger > 2 Amps).
Then the smart battery sometimes stops at 60 - 70%. So the best prevention is:
Shut down Android before plugging in the original Nokia charger.
Hope this helps ...