How many battles does it take to fully mega evolve a pokemon?

Sorry if this is a dumb question, but I would like to know how many times do I need to defeat a pokemon for me to be able to lvl 3 a pokemon? I seen some posts previously stating some megas require 10 megas before fully leveling up? But what about Mega Manectric? I won't be any top winner's if that makes a difference. I am not sure if dealing damage gives you extra mega candies.