Yup. Depending on the model you have, if there's a DC adapter, you can easily power it with a lithium battery pack.
I've done it it using two different packs.
I got two solid nights when using the dc adapter for my airsense 10, and turning the heated hose and humidifier off with this pack:
I bought this, and can power both my wife and my CPAPs for two nights (probably 3) using the same settings:
Basically, you'll need to find out how much power your machine uses when it's running, and how many nights you'll need to accommodate, and choose accordingly.