This is not the first time and i assume it wont be the last time but why in hell is Blizzard Update Agent using almost 90% of my CPU while it download things for the upcoming patch? Now its not often this happen but WHEN it happens, its annoying as fck
Im using a Intel Core i5 6600K, Asus Z170-E with 16GB DDR 4 Ram if thats to any help
Hey Granis,
Could you see if this persists after closing background applications and deleting the Battle.net Cache and Battle.net Files?
Have a few seconds to spare? Let me know how I’m doing!
Soon as the update is complete, it all goes back to normal. But why is your updater needing 90% of my CPU? This happend when Overwatch came out with a patch, same with Diablo, HS, HotS, SC2 i can go on but im sure you understand my point
I have the same problem — for several days battle net app has been trying to background download the 1.07GB patch… It is still at 0%, and the CPU is at 100% forever… AMD Ryzen 7 1700’s temperature now exceeds 80 degrees C.
I have followed ALL the advice in this forum and in google and nothing helped. This included deleting the programdata stuff, reinstalling battle.net, putting telemetry and cache entries into the host file, and more.
Why does this update need so much CPU, or why is this background download program so badly written? even its beta version is the same.
The laptop is useless while battle.net is alive… Sluggish as heck.
Just closing the app does not terminate the looping downloader in the background… Task Manager is needed to kill it.
I think this is because you have set download speed to some high numbs, or even no limit, when you download massive files with big speed your cpu is greatly used to follow everything what is going on, it’s not Blizzard - HDD only connection, cpu is used for everything, more data in less time, more cpu usage.
It shouldn’t be that severe. I can download a few GB Linux ISO and the system will barely notice it. Downloading itself shouldn’t be a problem, but the software around may be (especially when no progress is visible).
Essential actually got it almost right, it is not just the download, the mechanism behind how we handle data is a little more sophisticated.
Update Agent will only download files which are changed or new. So, instead of a full download of a new version of the archive containing the updated game files, just required data is pulled from the server. Imagine just a few files where changed: Instead of downloading the full archive, only the two files are downloaded and the archive is updated locally.
It keeps overall size of a download smaller, but this approach requires the local data container to be uncompressed, updated with the new files, and recompressed. Such tasks go heavy on the CPU, as they are processed as fast as possible.
If you run into a scenario, where the Updater is stuck at high CPU load, it is probably restricted and running in a loop; most likely caused by a permission issue or security software either containing the Updater itself or blocking access to the World of Warcraft-Folder.
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So it’s not the download itself 
Is it decompressing/compressing CASC files or something else?
I disabled the download speed limit and it actually downloaded in like half a minute… finally. It does use that CPU: https://www.reddit.com/r/wow/comments/b0cdw3/when_you_disable_background_download_speed_limit/ 
I just now noticed my CPU fan spinning up a bunch while I was just browsing the internet and saw it was the blizzard update agent that was the culprit.
Turns out that (for me at least) removing the download speed limit for patch preloading made the cpu usage drop. When I re-enabled it I could see the cpu use increase and hear the fan start to spin up again.
This lines up with point number 2 from this post: https://us.battle.net/forums/en/bnet/topic/20745536721?page=3#post-60
Strange that Blizzards own throttling mechanism would cause this though.
Can confirm that the same thing happened to me and turning throttling off fixed it. Might be worth looking into, as it’s clearly not being caused by the general patching mechanism itself and is still happening.