What causes the electric charges to flow from one end of the battery to the other

Electrons are very emotional and compulsive things. They feel

an intense desire to get away from negatively charged things or

places, and an equally strong desire to get closer to positively

charged ones, as if according to some law of nature.

By means of chemical things inside batteries that I don't understand,

one end of the battery is kept positively charged and the other one

negatively charged. So if there's anything between the terminals that

an electron can easily flow through, they'll do it!