How do you manage two phones? I also have two phones but one strictly stays at home...Surprisingly my voice calls on the Xiaomi doesn't last long even on 2G networks while GSMArena rated it 13 hrs talk time on 3G. I noticed when I had a 6 min 2G call, it killed 18% and my battery was 2% worse after an 1 hr SOT from a full charge. My voice calls might only last 5-6 hrs. I will test it turning 3G on while mobile data is off. I doubt it will make any huge difference.
Of course dual wielding phones can remedy all that. I also agree with Jon Rettinger who also uses a OnePlus One and thinks it has the best battery life he ever had on a smartphone (11 hr SOT). I tend to charge my phone every night anyway whether from 1% to 60%. As long as a phone can last ALL DAY without me charging up during mid-afternoons.
For my bare minimum, it should be 8 hrs SOT where I will find it respectable which is around the same time as a typical work day. If I am awake 16 hrs a day, I should hope the 16 hrs get split to work and my smartphone. The only smartphones that ever gave me 8 hrs SOT without breaking a sweat was the iPhone 4 & Mi 3. Almost every other smartphone I owned lasted 4-5 hrs SOT and needed a quick charge each day.
The BEST VALUE AND BATTERY COMBO for 2014 is OnePlus One and Sony Xperia Z3 Compact. That is a potential 25+ hr SOT between them and buying both (sub-$400) can cost as much as one iPhone 6. It is very most complementary to each other. Better than any Samsung Galaxy S5/Note 4, HTC One M8, iPhone 6/6 Plus, or Nexus 6 mix and match combo. The value and battery life is all there as well as big & small.