Yeah, I have the same battery for mine, it'll go about 2 nights without a recharge on my DeVilbiss machine.
Another option, if you don't want to spend big bucks on the portable Li-ion is to use your car jumpstarter. I often use that if we have power issues, or if i'm car camping. It's not terribly portable for a long hike, but it'll power my machine for 3 days without the humidifier with no recharge, and they are under 100 dollars. It can also be recharged from a running car, so in a long power outage that's an advantage.