Question

How does a battery create a potential difference in a circuit ?

Answer 1

A battery maintains a charge difference on the two terminals, in spite of the load (resitance in the circuit connecting the two terminals). The negative pole willl have a negative charge compared with the positive pole. The absolute charge on the terminals relative to some "neutral" reference depends on the circumstance, such as batteries connected in series. There's almost no chemical reaction in a battery until current starts to flow (the small amount of reaction is why a battery has a shelf life where it self depletes even without any external current flow). Once current is flowing, the chemical reaction tends to maintain the charge difference between the poles, although the charge difference and voltage will decrease somewhat as the load (currrent) increases.