Transit Card balance after removal from the wallet

If you remove a transit card from your wallet, what happens to the remaining balance on the card? Does it get returned to the physical card the funds were provided for or is the balance lost?

In China this is the easiest way to travel, but if I'm only visiting a city for a couple of days, buying and returning a physical card is a lot of effort. I'm wondering if funds on transit cards can be returned when you remove them.