Yes, Mickey Mantle did have a lifetime batting average.
Mantle's MLB batting average is .298
To compute his lifetime batting average, someone will have to gather stats from all of the pickup games, grammar school games, high school games ands the minor leagues and exhibition games Mantle played in - and then incorporate them with his MLB numbers. That could prove difficult.
http://www.baseball-reference.com/player...
Without looking it up I would have said .297. Looks like I was off by a point.
.298