Hi,
The E5470 was produced in 2016, if you have not had a battery replacement then it’s highly possible that the battery may charge to 90% but is no longer able to deliver enough current to maintain laptop power requirements.
You can also remove the battery and check voltage output to the charging tabs on the laptop to confirm that the charger is delivering correct voltage to the battery.
You can also check voltage on the battery itself to confirm what voltage it has when removed (90% reading before you removed it).
Hope this helps