We can agree to dissagree.
I am a journeyman electrician and have been dealing with batteries and chargers for 30 years.
You may think you are getting a full charge based on whatever readings you are taking but I can assure you you are not.
A charger designed to charge specific size batteries and used to charge anything other than what they are designed for is dangerous and it is irresponsible to recommend others to do the same.
I know first hand how dangerous electricity is and the deliberate missuse of any electrical equipment, including that wallwart charger, can have serious consequences.