With the Likebook Mars I got used to charging it often. I was exepecting the same with the Boox, but it has suprised me in a good way.

It came configured to power off within a couple hours when unused. Which is one solution. If you only read every few days, setting it to turn off when unused does ensure it will have juice to spare the next time you pick it up, though you'll have to wait about a minute to actually be reading again.

To avoid booting it all the time, I currently have it set to power off after 2 days of inactivity. Which is essentially never, unless I take a weeklong pause in reading.

This has meant I'm plugging it in once a week or so. Still more often than the month my Kobo used to last, but not bad at all. I can still empty it in one day if spend all day reading with the frontlight on, but that's true for any reader.

If I queue up a bunch of manga downloads, it can drain from fully charged to empty in about 2 hours.

When it does go unused, power off within two days means it only wastes about 10% of the battery sleeping before powering off entirely. (That translates to about 5% per day when sleeping, that's with network off during sleep and all apps suspended). Meaning I've not had to charge it when I go to use it after a longer break.

I don't use koreader myself, but it's on f-droid and hence extremely easy to install on the Boox.