Technically it is better for the battery to be between 4.10 to 4.19v, not full 4.2v, as fully charging them scratches away at their aging so to say. Yet the error I have noticed with my Nitecore is from a drained battery placed in bay 1, blinks a bit as the charger "Reads" the battery, then plop, stops charge with full bars though I know the battery is at 3.6 to 3.7v. Still the charging algorithm of the Nitecore chargers are the gentlest.