Is it possible to buy an "external" battery I can connect to my old macbook air 2008? I want to use it as a back up for a few hours when mine dies. Here is what the outlet looks like (attached). It also has 1 usb port. I have done research on Amazon to try to find something like this but it's very confusing to me what exactly I would be buying and and whether it would work on an old macbook air. When I post a question on Amazon I get all kinds of yes/no answers. Thanks! Kate
