The Sony's power brick is 19.5V at 3.3A. That's not exactly a standard thing for which you can buy a battery pack.

Amusingly, I thought the computer was asleep, since its screen was off, but instead it had apparently crashed, while sitting there, and I had to hard boot it. At least it boots fast. I don't have Office on here (despite having a bunch of stuff in C:\Program Files\Office15), but there is a PDF viewer that does 2-up and lets you swipe to advance.

It's too late today for me to start a battery drain test for you, but I'll give that a shot tomorrow.