The idea of spitting on a cell to give energy may not be very attractive or possible , but scientifically it is correct. The saliva or dirty water fed batteries are already a reality. A group of scientists from Binghamton University in New York, led by the researcher Seokheun Sean Choi, have developed disposable paper batteries that arerecharged with dirty water or saliva. Actually, the source of energy is the bacteria that contain these liquids.This battery has a curious origami ninja star design, which can be deployed to connect up to 16 batteries fed with dirty water or saliva. You can see it in this video:-
see link below for video
techxtra..co.ke/2017/08/see-battery-powered-by-saliva-video.html?m=1