According to numerous sources, The Dark Knight Rises will be the end of the Batman series. I think all the three Batman movies directed by Nolan was successful and did well at the box office. Since his great success in Batman series, Why did Nolan want to end the Batman series?
There are numerous magazine articles and interviews with Nolan in which he states that he always conceived his Batman films as a three-act story. He and his brother had the basic arc mapped out from the beginning, it was just a case of putting meat on the bones when the time came to write the next script.
Without getting into specifics, the key thing that makes the third film an great possibility for us is that we want to finish our story. And in viewing it as the finishing of a story rather than infinitely blowing up the balloon and expanding the story ... I’m very excited about the end of the film, the conclusion, and what we’ve done with the characters. My brother has come up with some pretty exciting stuff. Unlike the comics, these thing don’t go on forever in film and viewing it as a story with an end is useful. Viewing it as an ending, that sets you very much on the right track about the appropriate conclusion and the essence of what tale we’re telling. And it hearkens back to that priority of trying to find the reality in these fantastic stories. That’s what we do.
BTW - DC and Warner really want to move on with their attempt at a Justice League movie, and Nolan's Batman does not fit into that scheme in any way; the character would need to be rebooted in order to allow the more fantastical elements of the JL stories to be told - right now he is too grounded.
One of the worst things that can happen to a movie franchise, especially a really good one, is over-milking.
Some directors in Hollywood care about story, not just money (shocking, I know). Nolan is one of those directors.
Nolan had a complete storyline for it and had a set ending.
Fun fact: Nolan actually had wanted to end it after Begins and leave it to someone else, but was called back to do the other two.