I think it would depend how old they were, and if they had battery replacement. I would ask the seller about the battery, specifically. A new tablet will have a new battery that will last a long time before needing charged, whereas a used battery, depending how old the battery is, may only last a few hours before needing charged, and will continually decrease the older the battery gets. Refurbished tablets don't necessarily mean that the battery has been changed; may only mean that the tablet has been checked over and restored to original settings, and made sure everything functions properly.
I just got a new Kindle about a month ago, and the battery difference between it and my older kindle is crazy. My older kindle is a few years old, so it now only stays charged for just a few hours before needing charged again. My new kindle stays charged for DAYS.