Consider work being done on a positive test charge by an external force in moving the charge from one location to another. in this case, the potential energy (increases, decreases) and the electric potential (increases, decreases).

the potential energy increases and the electric potential increases

Explanation:

we know here that Voltage i.e. (Electric potential) increases from the initial point  to the final point

consider if 2 object of different charge 1 is twice the charge of other moveing in same distance in electric filed

than object of twice the charge require twice the force so twice amount of work

This work change the potential energy by  equal amount of work done

so electric potential energy is depend on the amount of charge on object

so if work being done on a positive test charge by an external force in moving the charge from one location to another

the potential energy increases and the electric potential increases

connect the batteries in series and hope