Yeah, sure, you could probably run a dynamo against the vat and get enough power to run a small light, bicycle style. But the contraption isn't powerful enough to do much more than that. So if they have ideas for which it really helps to have small amounts of electricity they could go for it.
Or they could let a human or animal power the dynamo, or a water or wind mill. A good water mill in particular is vastly more powerful.
On another note: how long would it take these guys to start their first war?
And not the first large fight, or the first murder, a full on "adapting your technology for killing other people, then going at it for at least several days, impacting every life in the affected area and ending a significant amount of them" war.
They should get at least a few generations in before that happens right, given their small numbers?