Interesting question. I have no personal direct experience (I make do with a Nexus 7 tablet).

This being said, there are battery banks with high voltage output. Add the proper cable and you are good to go.

Now, this will only get you a few more (8?) hours of autonomy. On the plus side, a battery bank is roughly the size and weight of a laptop charger. On the minus side, charging a large battery bank will take much more time than recharging your laptop using the charger.

Looking forward to reading updates on this thread