I’m gonna guess you’re asking a question that no one actually has the answer to, however a reasonable deduction would be, be reasonable with it.
I packed our slide out storage compartment full of fishing gear and misc camping stuff. 50lbs? Never gave it a second thought.
Plus the drawer/compartment on the inside was full of kitchen/bath stuff. And I’m sure the kids rode the slide in and out a few times, sitting at the table.
However it does seem like a silly place to store ones extra large pet rock collection, and putting batteries there just doesn’t make a ton of sense although it’s doable.
So to answer your question with a question, what are you considering putting in there?