bad in the sense of worn out, or because of their content?
Bad because of content or writing style.
"Worn out" would be a different word. Even in English, you would need to use something like "bad condition", "tattered", or "shabby".
I keep entering, "The books are very bad." but it keeps saying that I am incorrect?!?!
I keep making the same mistake. "The books are SO bad". It sounds correct to me.