There are a few reasons for this continuing problem:
- Power-demanding functions:
- Bigger & brighter screens
- High-speed mobile network
- Vibration notification
- WiFi & Bluetooth
- More use
- Ever thinner smartphones
The latest iPhone is always thinner than the previous version. Users like it that way. It's elegant and it's a proof that the device does indeed contain the best technology possible. It's prestige. It would be a bold step for Apple to decide it's not going to continue the race to razor blade thin devices. Someone will continue the race though, so Apple wants to keep up.
iPhone6 Plus has much better battery time than iPhone6. The reason is size. iPhone6 Plus is slightly thicker, but also higher and wider. That increases the volume considerably and that's one thing needed for improved battery time: more volume for the battery.
I came to think of my father's old Volkswagen from 1958. It had no fuel indicator. That meant you never knew for sure if you had enough fuel. It didn't even have a trip-meter, but it did have a mileage indicator, so if you knew the fuel consumption and you took note of the mileage indicator, you had a rough estimate of the fuel level. You could also shake the car and listen. And now comes the reason for this paragraph: the extra-tank-switch. You won't find it in modern cars. Say you run out of fuel. No problem: throw the switch and suddenly you had an extra couple of liters in the tank. It's almost like magic isn't it. I suppose there were really two fuel tanks in the car separated by a valve and at every fill-up both tanks got filled. The magical switch simply opened the valve so that what was in the small bi-tank quickly flowed into the main-tank.
Perhaps the extra-tank-switch idea could help getting better (perceived) battery time. It could work like in that old Volkswagen: "you completely run out of battery, no problem, throw a switch". It could also be a switch for quickly turning off/on a number of functions in a user configurable way.
There will always be parallels between old and new technology that can be of use.