Although I don't own this sound module. I'm assuming the two 9.6v batteries or 7.2vare recommended because the module was created to cater to RC battery standards.I'm willing to bet you could get that sound module to function on one battery, but you'll sacrifice the thunderous sound that it was purchased for.

As you said, thereal question is, "What's it's actual working voltage." It's obvious that it has a voltage regulator incorporated because two 9.6v batteries fully charged is roughly 21.6v volts in the first minute or two and two 7.2v's is 16.4v. If I had to make an educated guess. I think it has a working voltage rating of 12v.</p>