I’ve noticed that when the battle.net app is downloading an update for itself, Activity Monitor shows CPU Load shoot up for both System and User. This time each went up at least 30% until the download finished.
This can’t be good for the computer.
I don’t think the System CPU is supposed to go up at all.
That seems normal given the Battle.net Agent is handling the download and installation. NOTE that during the end of download/patching the client is also installing data. If you believe something is off though I recommend posting over on the Bug Report forums for our QA and Developers to look into Here.