Where can I buy original Xiaomi products - battery and headsets in Xian?

You may go to Xiaomi Store to get what you want and the store is not hard to find in the city. I happen to know one at No. 26, Anban Street. Take metro line 2 to Bell Tower Station, Exit D. Walk east along West 1st Road for about 300 yards, and turn right. Walk south for about 100 yards to it. :)