My Philips Restonic (sp) is a 12 volt unit, which I think most are. So all I needed was the 12 volt cord. In the TT I installed a 12 volt cigarette lighter plug in beside the bed. I'm yet to do that in the TC, it's on The List. Right now I use the Optima 24 AGM from my trolling motor and a clip-on cord with a cigarette lighter plug end. Optimas don't spill. I'll be using that cord in OZ in couple of weeks, too. At the clinic they sell 12 volt batteries for the machines. They look like a 24 AGM battery. They claim 24 hours use from one. I hope my experiences help with your sister's travelling.