Old lithium jump start value.

About 6-8 years ago Menards had a really cheap sale on jump start batteries all I remember is it was really cheap.  No recept. It's down to 65% charge now  when plugged in.   If I pull the battery out and use it in the challenge car what's  fair?    
  No I'm not going to document, it I just want to know for my own.  
    I'm too cheap because I know if it was for sale at a garage sale anything more than $15 bucks I'd walk by but maybe I'm too cheap?  

I'm pretty sure that's a lead acid jump box. 

The battery inside that is probably a 12v Sealed Lead Acid to the tune of 9-12Ah and is probably worth all of $10 used.