What smartphone has the longest battery life?

Question

A battery that can last more than 1 or 2 days, and also can be changed.

Answer 1

I vote for the YotaPhone 2, with a second E Ink display.

"According to Yota, 15 percent remaining battery will keep you going for eight and half hours of runtime on the E Ink display" - says the Engadget review 

A Lenovo S860 has a 4000 mAh battery, but it's not user replaceable.

The Huawei Ascend Mate 2 has also a huge battery, not sure if it's user replaceable.

Answer 2

I go for Sony Xperia Z3 because it has a battery capacity of 3,000 mAh. The Xperia Z3 is another smartphone in the 2-day battery life camp, often capable of hitting this benchmark with juice left in the tank. Unfortunately, Sony's omnibalance design means that, although the Xperia Z3 is water resistant, its battery is not removable. We also can't comment on how the Xperia Z3 battery will perform with the PS4 Remote Play feature. Nonetheless, it's still one of the best performing batteries for specs it houses, with 3 GB of RAM, Snapdragon 801 processor, and 5.2-inch full-HD screen...

Answer 3

Nokia smartphones and even way back their analog phones, the brand has always been known to have the best battery life span.  Also blackberry units.