I came across some of my son's books from when they were little. They are the "sound" books. One even has a steering wheel on it (titles link to amazon info). Are these able to go media mail or because of the sound they are not able to? Also, I have extra batteries, can I include those as well and should I remove the battery already in the book before shipping?

Thomas & Friends Steering Wheel Sound Book: Ride Along with Thomas

Baby Einstein: Lullaby Classics
 

You can definitely send the book. See below 'media mail description from USPS.'

Does the book come with the batteries or did you have to purchase them separately?

From www.usps.com:

"Media mail® service is a cost efficient way to mail books, sound recordings, recorded video tapes, printed music, and recorded computer-readable media (such as CDs, DVDs, and diskettes). Media Mail can not contain advertising except for incidental announcements of books. The maximum weight for Media Mail is 70 lbs.

Sending anything other than that described above by Media Mail postal rate is illegal. 

Media Mail packages are subject to random postal inspection and if a package is found to contain unacceptable items/materials, the difference between first-class (or priority rate if the package weighs over 13 ounces) and Media Mail postage will be assessed.  Packages that are found to violate Media Mail postal rate may be returned to the sender, OR they may be delivered postage-due to the destination address.

The books came with batteries and I had purchased extra from the companies directly to fit only those books so I have the extra battery for each as well.

This is also from the rules:

Books that require batteries to work do NOT have to have working batteries.

So, you don't have to include any batteries. I believe that you can include the batteries that are installed in the books ... and it can go media mail. BUT, the seperate batteries probably cannot be included in the package.