Well a battery powered halogen torch like a maglite comes to mind.
However a typical AAA battery has a capacity of between 0.3 and 1.3 Ah (or between 0.8 and 1.8 Wh) depending on the chemistry used in the battery so we would need something like 10 or 20 of them to power a 20W halogen bulb for 1 hour I think.
I suppose it would be a bit of a squeeze in there for so many. I suppose the maximum capacity could be 2.
Unless they are rechargeable but then i think it would require the supply voltage and current to be sufficiently high to recharge them about 10 and 20 times an hour. So the supply power would still be relevant and even so I'm not sure if such battery could be charged and discharged in say 6 minutes?
Its interesting to consider but I think it is very unlikely that it is possible for an internal battery to account for the thermal power seen however.
If viable though it maybe important to check the parameters of the demonstration test eliminate this possibility of internal batteries or external charging of any possible internal batteries accounting for the total thermal output
Could be cool design though if the E-Cat QX is somehow able to recharge two batteries and those are sufficient once charged to initiate the process.