While there's plenty of debate about their execution and his culpability, Ben Affleck's Batman in Batman v Superman: Dawn of Justice is directly involved in the deaths of 21 people, according to Mr. Sunday Movies's recurring Death Count video feature.
Most of it comes from the Batmobile chase sequence, in which Batman dragged cars around, hurled them at one another, shot them up, and ran them over with the Batmobile. That's 13 bodies on the ground just in that scene alone (and no, the video doesn't count the Knightmare dream sequence deaths of the Superman soldiers as part of the eventual tally, although they do count them, and then zero it out when it's revealed that the scene was a dream sequence).
21 might sound like a lot of people killed -- and of course, it is, especially for a character who has made a no-kill pledge such a big part of his identity in the comics and in Christopher Nolan's Dark Knight trilogy. For comparison purposes, a similar video by Lucky Six Productions blamed Batman for 14 deaths in that whole trilogy, although to be fair they counted a lot of elements in the Batmobile scene from Batman v Superman which wouldn't have been counted in Batman Begins, for instance, where Batman likely (but not explicitly) caused a number of traffic-related deaths and the two police officers that seemed pretty clearly dead as a result of his initial Tumbler assault later reappeared on camera.
Still, it's the same number over the course of the movie that Iron Man killed just during his escape from imprisonment at the start of Iron Man, which saw the Armored Avenger eventually kill at least forty people.
(For comparison's sake, The Dark Knight is seen as killing 17 people in Mr. Sunday Movies's Kill Count video for Tim Burton's Batman, as well, and 29 total between the four Burton and Schumacher films.)
Fearing the actions of a god-like Super Hero left unchecked, Gotham City's own formidable, forceful vigilante takes on Metropolis's most revered, modern-day savior, while the world wrestles with what sort of hero it really needs. And with Batman and Superman at war with one another, a new threat quickly arises, putting mankind in greater danger than it's ever known before.