Or just put a decent size battery in, seeing as they increase in capacity by 5% a year on average we haven't seen the battery increase in phones.If only the days of batteries been removable came back.
With larger battery means you can implement battery managment. To vastly extend life. But they don't care about that as they want to sell newer phones.
I have a P2 5000mah battery. Means I can charge to 80% and still last most days easily. But nothing built in and automatic for that, have to use a battery alarm and unplug it.
They could also implement smart charging, when charging overnight it doesn't need to be fast, which means you could charge slower and lower battery temp, which is another thing that kills the life of lithium ion.
Removable batteries are a headache for things like waterproofing a feature I would love and is on most high end phones these days.

