Xperia Z2 (Kikat 4.4.4) - STAMINA mode does not work?
I think they renamed the Eco mode controller app with the 4.4.4 update to Stamina mode...  So scroll down until you find that app. Take note of the estimated days and hours before you force stop, clear cache and restart your device. 
activate stamina mode again after boot and note the change in estimated days and hours. 
Hope this helps!