Transcend P8 multi-night Battery Pack

I bought one of these in order to be able to use the Transcend CPAP while camping. It is advertised as multi-night, but I don't get even one full night - I actually get about 4 hours. I returned the first one and according to CPAP Sales it performed to spec on bench-testing. The replacement performed the same for me. It may well go more than a night on testing, and perhaps with low treatment pressure and under ideal circumstances, but it was not a viable solution for me. I use it when there are power outages at home, because even at 4 hours that will usually get me through a blackout, but for camping I have had to go to alternative solutions.