My zapper is about a couple of years old. When i first started using it I had the effects of tingling, twitching and other movements inside the body. I consider that an indication that parasites and whatever were being killed or that the positive charge was penetrating my organs and blood etc.
Now I know when my battery is low, I feel nothing. When I have a new battery, I feel it. Even though mine is still good, I want a new updated one soon, because they are always being improved and I want to keep up with it, especially when people around me are getting cancer.