I recently had a Porygon 2 which was awesome for battles. I had to attack very few times before the charged attack was filled and the charged attack was really powerful.
I evolved it to a Porygon Z and after that I had to attack several more times before the charged attack was filled. The evolved pokemon was considerably worse than the lower evolution.
I have also noticed that when battling other trainers, some of their Pokemon can send of several charged attacks, while I get almost no charge to my charged attacks.
So my question is: What affects how much/how fast a charged attack is charged?