What currency do you charge in?

Overheard at the reception desk on the Queen Mary 2:

German gentleman: “Good Afternoon. I have a digital camera with a rechargeable battery——”

Receptionist: “You can get batteries at our camera shop, sir.”

“I have a rechargeable battery, so I don’t need to buy batteries. I just need to charge it——”

“You can use your ship card to charge batteries, sir.”

“Yes, thank you, but what I want to do is use my battery charger in my stateroom, but it’s not working. What is the currency on this ship?”

“We use U.S. dollars, sir.”

“No, the currency to charge my battery with——”

“You can use your ship card in the photo shop to charge batteries.”