Alright, just to stop people from accidentally wasting pages as I have trying to figure out how exactly this tome of fire works...

When you get a new tome of fire, you have to charge it with burnt pages. You only need 10 pages, you use the pages on the book.
You now have a tome of fire with unlimited charges in it.

After you have charged the tome of fire, there is a "check" and "pages" option upon right-clicking the tome.
The "pages" option will revert the item back to "tome of fire (empty)" and return only 1 of your 10 pages.

If you accidentally do this, DO NOT USE YOUR PAGES ON THE BOOK because it will require a full 10 pages to charge it again.
INSTEAD, click the "pages" option on the tome of fire again and it will fully charge your tome with only 1 page that it gave you back.

Credit goes to Ipoy Gimp for helping me figure this out - thanks again