I am travelling to Europe next week and will be travelling on the road quite often. I would like to get some work done during that time. My laptop battery will inevitably run out of power during that time and I would like to carry an additional power source with me so I can get some extra juice when I am nowhere near an outlet. I have the latest MacBook Pro where the battery is not removable. Where can I get an additional power source for my MacBook Pro? I don't mind if it is a 3rd party product.