I've been doing some research that is associated with the possibility that I might sell my current MacBook Pro (2010) in order to buy the current one with the Retina Display. I've been browsing completed auctions on eBay to get an idea of what my current MBP might sell for. In the process of looking at these auctions and their descriptions I noticed a peculiar characteristic about the notebooks being sold that I have not heard or considered before; i.e. battery cycles. Many of these auctions that I've looked at make references to how many battery cycles the notebook has gone through. So what is this battery cycles attribute about? How can I tell how many battery cycles that my notebook has been through?