answer: #Person2# has #Person1# changed the battery of #Person2#'s watch.
documents: #Person1#: What can I do for you?
  #Person2#: Yes. There is something wrong with my watch. It stopped several hours ago.
  #Person1#: Let me have a look. Oh, the watch's battery is worn down.
  #Person2#: How much is a battery?
  #Person1#: $ 50.
  #Person2#: How long will it last?
  #Person1#: About 2 years.
  #Person2#: Here is the money.