I never measure my battery usage but I read enough on phones that I'm aware of the battery drain. I do most of my reading on my phone with Moon+ and I do some with the Kindle app. Both are tough on the battery but Moon+ is definitely harder on it. I haven't used other apps enough to know how they fall into this.
I got tired of using up my battery so fast on my phone so I bought a cheap phone just for reading. It's the 2018 model of the Galaxy J3 Orbit. It's $50 on Amazon. I don't have service on it. I just use it for reading. It fits nicely in a pocket. I'm finding that I really like it better for reading than my Galaxy S5. Here's a link if anyone is interested:
https://www.amazon.com/Tracfone-Sams...gateway&sr=8-3
It also has a user replaceable battery.
Recently I noticed that my S5 has a power saving mode so I turned that on and now battery drain isn't a problem anymore. I can read on it and my battery still lasts all day. I don't know if other phones have that feature or if they work that well but this has made me wonder if I still need the J3. I haven't decided yet what to do.
Barry