What happens to a Batarang after it's used?

In the DCAU, Tim Drake manages to retrieve one and teaches himself to use one before he becomes Robin. So presumably Batman doesn't keep track of them there.

And there's apparently an issue of Teen Titans where Tim also says he was able to hide the cost of shipping a Batmobile across the country in the batarang budget which is "larger than you would think" so he might not do it in the comics either.

If I were writing it, I'd go with the idea that he'll retrieve them when he can and he has some kind of web trawler that picks up people selling them and buys them under the guise of an anonymous collector.