My Samsung Galaxy S5 has an "ultra power save" mode.
Turns off almost everything, leaving only phone, sms, camera, calendar, and grey scale screen.
At 100% charge it claims 14 days life - haven't tested that.
When I want Google Maps or some more powerful feature I simply drop out of that mode... One screen swipe and one screen tap.
When I am done, back to ultra power save mode.
Best of both worlds I reckon - Power when you want it and battery life when you need it.