I have used it a full night (8 hours and 53 minutes) to power my ResMed Autsense 10 Auto machine. I had both the humidity and the ClimateAir heated hose operating on Auto. About two thirds of the water in the humidity tank was consumed.
After the full nights use as above, it took 17 hours to charge the battery back to full charge at 1.25 amp hour rate. Battery Tender has a 5 amp hour charger available. I may order one of those. The 5 amp charger should charge it in one fourth the time which would make it more viable for multi night use.
I was using the 12 volt to 24 volt converter that is produced by ResMed. I intended to experiment with a voltage converter I rigged but the ResMed converter is superior. The ResMed converter has a circuit that will turn the converter off before it drains the battery to damaging levels which is a handy. Also, the ResMed converter converts the voltage very efficiently. The overhead power consumption was negligible. Much better than converting 12 volts to 120 and then back to 24 using an inverter and then using the normal ResMed plugin charger.
I will update as I get more experience with this setup.