To charge or not to charge a card

Almost every week, I hear one of my German colleagues say

I have to charge my card

just before we go to lunch in the canteen. Interestingly, this means essentially the opposite of what they mean to say. When you charge a card, the card owner will have less money than before. What my colleagues do when they “charge their card” is to put money on the card, to top up their card, or to load their card. Another expression with the same meaning would be to add money to their card. The confusion may arise form the fact that in German, you use the verb aufladen in this context, which translates to “to charge” in English.