I'm not the OP, but when
my feature phone battery lasted a week, I made some phone calls every day or two, and used the phone as a daily alarm clock.
If Google Play Services decides to not burn all of my battery in busy waiting or whatever, and if I make zero phone calls and have a daily alarm, my smartphone battery will last between two and three days. When my phone was new and I was commuting with it, I would typically get between eight and ten hours on a charge.
I would happily double the thickness of any modern non-ruggedized smartphone in order to double its battery life.