Like MetroCard in New York, they provide travel card which you can pay fairs through a prepaid card. But after some uses, the money inside the card decreases and you need to put more money into it. Let's say you want to put 20 dollars more in it. How do you ask that requirement to a staff working in the subway? I may use sentences such as I'd like to recharge 20 dollars, I want to top up my card 20 dollars, I want to reload my card 20 dollars.
What expression do you use usually in everyday life?