You could had set the voltmeter to 'volts' placed the prongs from the voltmeter onto the prongs of the resetter and measured the voltage though i accept to an electronics expert such as yourself that entirely obvious course of action is not a obvious at all.
If you have no intention to ever use one again there is nothing anyone can do to assist you further. (as predicted the too much effort answer)
Instructions for mine are very clear and accurate, including light flashing info, it is a rock solid product which just works. As to yours failing i accept you had issues and nobody else here has.
I imagine some forum members would be very interested in the internals of that resetter, most battery ones i know of come with a single CR2032 battery. (Ive seen one that used AA or AAA batteries but never 3x small cell types) If you could post some pictures some forum members will find them very interesting.