It certainly shows the potential for mobile Linux for sure. There’s a project https://postmarketos.org where you can install their mobile Linux OS on Android phones if you want to give it a try on a spare phone or something. The wiki lists what phones the OS can be installed on and what hardware features are working for each device.
When the phone is not set to suspend, and mostly idle with a couple of apps running, and some occasional web browsing, its about 4 hours. Under similar conditions using suspend (meaning it will keep the modem powered and wake up the rest of the device wen receiving phone calls and SMS) then I can get through a 9 hour workday and have about 40% battery left.
I have been daily driving the phone for a couple of years so I’m sure the battery has degraded some, but I don’t know how much difference I would get with a new one. It can be easily replaced, so I may do that in the future.