I think its all in his head to be honest. Im 1 year from graduating with a degree in electronic engineering , and even i cant see how there could be a difference! , batteries are DC .... so its not as if one will give a cleaner signal than the other . Plus, lets say one duracell has a voltage of 9.1, and an energizer has 8.9 V , well i`ll swear that the next energizer will have 9.1 V and maybe the next duracell off the line produces 8.85V
They are all gonna vary somewhat , so anyone who claims they can tell the difference between two nine volt batteries is smokin too much! ........ in my opinion