I've got an Alpkit Numo thats a fair few years old but has barely been used. I tried using it last October but it had deflated by the morning - when I looked at it the other day I saw that he valve block had become unstuck from the fabric which is quite common.
So I fixed it with AquaSeal and it's done an excellent job. I left it fully inflated from last Wednesday to see what happened and by Monday evening it had lost about 30-40% of it's air and was a bit soggy.
Should I expect it to stay inflated longer or is this about right?
(I also repaired a couple of holes in an old Thermarest and that seems to have stayed fully inflated which is pretty impressive.)
No - IMO it shoud stay inflate4d much better than that - if its going down with no weight on it I bet it goes down quicker when you lie on it
I'd blow it up, stick it in a bath of water and see put some pressure on it to see if it's leaking. It doesn't take much to lose air over time. If it is, try resealing the leak site.
I had an Alpkit Lumo once that did this. I don't think they were made to last sadly! I suspect the residue from breath degrades them from the inside. I didn't get much use out of it before I gave up on it after a few uncomfortable nights.