Hi,
I have recently moved from iphone back to Android getting the LG G2(amazing phone!) and was having the exact problem of quick battery drain, with Android system account for 50-60% battery usage when checking battery stats and losing 4-6% battery per hour with the phone screen off and quicker drain when screen on. Being an old android user I knew something was amiss.
Follow your recommendations on this thread I installed GSam and found Android Kernal was accounting for 60% battery drain. After a bit of digging around on forums Google is indicated to possibly to be the culprit. Therefore I went to google settings via the app and done the following;
Connected apps > disconnected all apps bar mail. This seems to have no negative effects
Location > Turn OFF location reporting. Google play service + low battery use (not sure what this is)
Search and Now > Google now turned OFF, Phone search = no change,
Search and Now > voice> OK Google hotword detection > Turn off (think the phone is always listening for a voice command.
Since doing this last night I can report;
7hrs of phone sleep/standby and only 1-2% battery drain total
8hrs moderate use today and I'm on 71% remaining (massive increase before the changes. That includes out in the fields in low signal areas (I'm a farmer).
Sorry for the essey, hope this helps someone
Android kernel and android system still seem to be high up on usage stats but drain is soooo much slower. It may well be this is just something that is the norm for kitkat, but losing just 31% in 8 hours will about do me