I have an adapter that came in two pieces. One has a 12V plug (cigarette lighter) and the other piece has a 12V receptacle that fits on the first piece and then has two clips to hook directly to a battery. Depends on what I'm doing and where I'm going as to how I use it. One note is that the humidifier, at least mine, will not work without shore power. Never noticed that this was a problem though, there is usually colder air surrounding the tube so the moisture in your breath keeps things humid enough. There are newer CPAPs made with camping in mind too. I find that when I use a separate deep cell just for the CPAP I only need to recharge it after 2 nights.