There seems to be a bit of confusion as to which Dorcy light he has. [Some posters mention 3AAA's and others mention boost circuit.]
He stated that its a Dorcy Super 1 Watt. Well Dorcy makes 3 models of 1 watters that uses that term, the 3-D, the 2-AA, and the 1-CR123 models.
I am guessing it's the CR123 model, since you mentioned the circuit board. [IIRC, the 3D only has a resistor?] and the 2AA isn't readily available in the states.
If this is correct, HarryN sounds to be on the $$ about the wild readings.
The Pulse wave forms could provide weird readings and the boost circuit at times provide high VDC readings under various loads.
Hope this helps,
Danno
ps I, too, am your amatuer electronics guy