could Greek discover electric battery and use it for medical purpose?
what kind of battery could ancient world could discover in easy way as gunpowder?
I'm not sure what medical purpose they would use it for. But accidental discovery of an electric battery wouldn't be too surprising. All you need is a container of some kind of acid with two different metals inside.
If the two metals happened to touch, they might generate a tiny spark. Or if this happens in proximity to a compass (or some piece of iron that happens to be able to turn freely), someone might notice that something weird happens when they touch.
But in the absence of knowing any theory about what's happening, I think that's about as far as you would be able to go. I don't think there would be any practical application, even if they figured out that they could attach the two pieces of metal to a long wire and get the same effects at a distance.