Have you ever had a Laptop and left it plugged in 24/7 at a desk as a work station?
My wife did that with her previous Laptop and then was shocked when she Traveled with it and the battery died within 30 minutes. In two years it went from 5-6 hours of usable power to just 30 Min.
This has been a limitation of lithium batteries from day one.
As for Ecoflow and all of the other portable units, they are of course not going to mention that limitation.
They often times show people using it on camping trips etc. With that kind of usage you can charge it just before the trip.