Should I cite a book that I read to prepare for a talk but did not directly use it?
What is the purpose of your talk?


If you are reporting progress of your work, focus on your work. In that case it is typically not relevant which general resources you used to brush up your understanding of the topic. 
If the purpose is at least partially teaching, I'd put them into a "Recommended Reading" slide / part of a slide at the end of the presentation.