The sonic screwdriver is known to do many things (well, as long as it's not to wood). But at the beginning of The Age Of Steel, the Doctor destroys a good few Cybermen by blasting something out of the screwdriver. Any idea how to justify that? Any other examples of the screwdriver having a bit more power than expected?
It's not the Sonic Screwdriver. A minute later in the episode, Rickey asks what that thing was. That thing being ... nothing. It's tiny. One of those insignificant little power cells that no one ever bothers about, and it's clinging onto life, with one little ounce of reality tucked away inside.
It's a Tardis Power Cell that the Doctor and Mickey find half way through the 1st part of the Two-Part Cyberman series, Rise of the Cybermen. After the Doctor finds it, he charges it with some of his life force (I just gave away ten years of my life. Worth every second.).