[toomuchtodo]

They traded function for form. Smaller batteries to make the phone slimmer mean less tolerances for charging and discharging (depth of discharge), causing short battery life (for the inverse, see Tesla; big batteries means less need to max charge or discharge, which means battery packs that last for a decade).

[textor]

It's funny how nowadays (for a few iterations, actually) Apple's phones have bottom of the barrel battery life, even facing severe degradation in a few months, yet the reputation from 4S and earlier lives on. I know many people who still believe that Android phones suffer from faster discharges.