Batman: Arkham series: Zero kill beat-em-ups?

This one crossed our radar when we stumbled on a article, which surprised us by stating that Batman never actually kills any of the swarms of villains he busts up in these critically-acclaimed action-adventure video games.
We're no expert on Batman's legacy, but apparently there was once a tradition for Batman to avoid killing any of the enemies that he was obliged to beat up in the course of his heroic duties— including even his arch-enemies like the Joker. This was our impression from glimpses of the retro Batman television series episodes that used the "BAM!" or "POW!" splash-screens to bowdlerize the implied violence in fight scenes, though later films departed from the tradition.
Either way, regardless of what the films allowed: Apparently there are multiple "Arkham" series Batman games that not only involve the option to win with zero fatalitites, but according to an article on "...go to great lengths to make sure you can’t break Batman’s “one rule,” including putting invisible walls up when you try to push enemies over a ledge."
Zap! Bam! Pow! (But no fatalities, according to contemporary accounts.)
It might take us awhile to get to this series, since they still sound like overtly violent beat-em-ups in which the no-kills rule is already built into the game universe (i.e. without the added fun of making a special effort to avoid the violence). However, we've also heard that the games incorporate stealth gameplay, so maybe we'll take a look later on and see just how nonviolentally Batman can solve Arkham's crime problems...
Zero kills built-in sounds great... the next question is how little violence can be used...