Like I said before, I'm one of the obsessed ones related to battery so I can tell you that I know what I'm talking about and know my phone behavior very well, been monitoring this for 11 months I can assure you that it has been extraordinary consistent and extremely good on battery life, best phone I've had related to battery. Then it came the Kit Kat update, and without changing anything on my network environment, and a full phone reset for the update, since the save day I updated I've been having the issue presented on this thread.
So I decided to troubleshoot this and what I've found after 2 weeks tests is what I mentioned here, only thing that had stopped the huge and new Android System high battery usage is turning the Wi-Fi off, so, I'm just passing my findings here so others can try, if others have the same results than me, then we can assume that something has changed with the Wi-Fi on the new update and maybe we can let z Samsung know about it.
Anyway, I just pre-ordered the S5 so I'm just having my S4 until the new one arrived, after that, if it was something with just the S4, it's on you to keep it trying to see what maybe different or wrong now.