What exactly is this Xperia Smart Stamina I hear about?

So, Sony announced a bunch of new smartphones at MWC, and among them is the top-tier, 4K HDR phone — the Xperia XZ Premium. A direct sequel to the first-ever 4K smartphone — the Xperia Z5 Premium — the new device comes with a modernized design and cutting-edge hardware, though, it had fans disappointed when it was revealed that its battery is actually smaller than the one on the old Premium. Namely, the new device sports a 3,230 mAh juicebox, 200 mAh shorter than the one on the old model.

Still, it's a respectable cell in its own right, and Sony promised that ...