he thinks the voltage is created by low-energy beta electrons emitted by cold fusion in the lattice.
Just a little comment: nuclear electrons (beta) cannot generate a net charge unless they are ejected from the lattice into free space.
Devices designed to generate charge from alpha or beta emission rely on the particles leaving the host material, traversing a vacuum, and depositing their charge on a collector plate.
If I recall correctly, LECs don't create a potential difference if there is a vacuum between the electrodes. So if there are any low energy nuclear electrons, they must be fully trapped in the lattice - and won't develop a net charge.
Nevertheless, something seems to excite the gas in a LEC. If the atoms in the WE are excited in some way (by whatever mystery process) then there has to be some coupling mechanism between the electrode and the gas. That mechanism could involve EM waves/photons - of unknown wavelength - or it could be something more mysterious.
I guess looking for the photons is a start. However, if there, they must be of rather low energy - or they would have stimulated some thermionic emission (and hence voltage) in vacuum LECs (depending on the work function of the WE surface, of course).