Re: "It's presumably converting its mass into energy."
My calculations suggest it is really converting mass to energy:
The average energy output was 816 Watts - this was calculated using questionable methods but importantly the control (dummy cylinder) when fed with 810W produced a very similar temperature.
The average power input was 235W, the test duration 116 hours.
Therefore the device showed a nett energy output of 67kWh or 243MJ. simples.
The reaction chamber volume was quite small - a 5mm bore 33cm long.
The secret powder that was in there was measured as 0.3g only - barely a coating. The researchers rounded this up to a figure of 1 gram. I will evaluate also a worst case figure of 57 grams - if the bore was packed with solid Nickel.
The energy densities are quite astonishing, considering petrol is the most energy-dense common substance at 50MJ/kg, with hydrogen (in any phase) on its own at 145MJ/kg.
I calculate 800 Giga-Joules/kg if the 0.3g figure is to be believed.
My minimum (using 57g) is still 4200MJ/kg - about 29x solid hydrogen.
the researchers claim 183600 MJ/kg - with a few other worst cases in there, I make it 242GJ/kg.
It could be all down to "fiddling the electric" - but it cannot be down to stored energy in the device.