Here’s what I ended up with, can confirm it’s working well with my DN:
Poweradd Pilot Pro 2 23000mAH: https://www.amazon.com/gp/product/B015OAJFOC/ The battery is fairly big as far as length and width (around the size of a paperback book), but not terribly thick (about the thickness of 2 iPhones). I had to figure out how to get it into 12V mode (hold down the button to get to voltage toggle), but once I got that sorted out it was fine.
It comes with a DC cable and an adapter set. The adapter set mine came with includes a plug that fits the DN, but I recall seeing a post from someone who’s didn’t, and the listing itself doesn’t indicate that there’s a compatible adapter included. If you need an adapter plug, here’s an option from Amazon that I can confirm works: https://www.amazon.com/gp/product/B01N812NKL/
Or, you can just get this cable so you don’t have to fuss with adapters (this is what I’m using now): https://www.amazon.com/gp/product/B00M7OE1VG/ (the right angle plugs aren’t my preference, but they work fine).
I haven’t done a full drain on the battery yet, but based on what I’m seeing from 2-3 hours of use, I’m guessing I’d get 8-10 hours of use from a full charge.
Hope that helps!