I agree. At least an optimal extended battery would be nice.

Nevertheless, I think that the problem with current smartphone batteries is that the leap from a day of use to a little more than one day loses the convenience of charging it at home at night.

For example, I'm used to charge my iPhone at night in my bedside, and the iPhone lasts about a working-day of charge.

A battery that lasted 1.5 days would not be as useful, because the battery would probably drain somewhere where having access to the battery charger is not as convenient as the one plugged at your bedside.