I don't have a stall warner......I imagine electric ones stop working in the absence of electrickery.
I would say though that this is a secondary piece of equipment, and not really nescessary in my view, other than for the JAA PPL
When I bought my plane, I didn't even notice that it didn't have one to tell you the truth, and I find them slightly annoying, especially if they're constantly chirping away at 5kts about stall. I suppose it can be quite satisfying when you touch down with the thing chirping away, especially on your YouTube vide
Anyway, not having a dig at anyone here, but I don't even listen for stall warning on landing (partly because I don't have one
) but feel the aeroplane and it'll soon let you know when it wants to stop flying....Just don't be too high at that point!