Stamina battery mode was removed from Sony Xperia devices with Android 6.0 Marshmallow upgrade and it is replaced by new “Doze” feature of Android. However many users become unhappy of this change as the new function was not as efficient as Stamina mode for many.
Yesterday Sony replied to my tweet about this issue with good news. Stamina battery mode will be re-launched in 2016.
Users who miss those functions have to just wait in patience.
Meanwhile I will personally keep “Doze” mode always on.