The 40-year-old actor found it "ridiculously unheroic" to need assistance getting in and out of the tight rubber suit he donned to play the Caped Crusader in three movies, so has advised his successor - who portrays the iconic character in the upcoming 'Batman v Superman: Dawn of Justice' - to check he can relieve himself easily.
Explaining the advice he has given Ben, Christian said: "The first one was, 'Be able to take a p**s by yourself.'
"I found it to be ridiculously unheroic between takes when I said, 'Excuse me, I need to pee, could somebody undo me please?' "
And the 'Dark Knight' star also told Ben to insist his mask wasn't too heavy or uncomfortable.
He added to The New York Daily News newspaper's [email protected] column: "I took three people 20 minutes with tools in order to take that cowl off [my] head."
Though Christian isn't upset someone new is playing Batman, he admits he is surprised a new movie is being made so soon after his last outing as the masked vigilante, which came in 2012's 'The Dark Knight Rises'.
He said: "The baton has been passed, that's the nature of Batman.
"Of course, it was passed a lot quicker than I expected, but I completely understand."