Batman is paranoid. So paranoid he formulated backup plans for every member of the Justice League if they were to turn evil. If Batman and Flash were to fight, Batman would have a fighting chance...if he could get to the machine in time. If he couldn’t bolt the bomb to Flash’s arm, then he would be defenseless against Flash’s superspeed. Also, he also has ice to temporarily disable the Flash’s speed, but he can still fight extremely fast. He can still punch one billion times in one minute. Batman, even though he is strong, and a master in all martial art, he still cannot match the speed of a raging Flash. Nobody can.