An e-reader battery lasts longer than a phone. Also, there are no temptations to constantly check news or social media (or even Amazon’s ecosystem: my Kindle has been in airplane mode since the very minute I unboxed it). I don't even take my phone into the bedroom because it is a proven source of distraction and poor sleep, but a Kindle allows me to do some long and productive reading at night or when I wake up in the morning.