Stefonius, If you are using 12V, why do you need the power brick?? Unless you CPAP uses other than 12V input?? All my poser brick does is to change 120v to 12v. I am aware that some machines require other than 12v. And some folks use an converter to change 12v to 12v, then plug in a brick to change it back. My 12v outlet is on the bus from my Mh inverter, therefore doesn't care whether the power is from the battery or the inverter. With my two 12 coach batteries, Mine will run at least two nights, but I don't use the humidifer in the MH.