How to read long, nonfiction books?

Hey everyone!

So relatively new to reading as a hobby, picking it up last year. I read 70 books, most of them fiction. Any non-fiction I read was quite short and I was able to finish in a few days. I read everything on my e-reader.

Now, I want to read some longer non-fiction books, such as letter collections, long history books, etc. In general, I want to read books are not conducive to reading all in one shot.

However, I find myself having trouble making any real progress on these books because, when I open my ereader, my current fiction book instantly pops up and I just keep reading that. It's a little too convenient in that way.

If any of you read longer books over a long period of time, how do you manage it? Maybe set aside time on the weekends, or read a few pages a day from each long, nonfiction/nonnarrative book you're hoping to work through?

Thanks :)