Flukely tire pressure monitor

I would leave the spare over inflated. You can adjust it if and when you need it. My pressures are different from front to back so I inflate to the higher pressure. I can deflate if I need it on the lower pressure location.

I never expect to get "accurate" pressure reading from tire monitors, but all I care about are "relative" pressures, i.e: changes. Most of mine read 3-4 lbs below actual pressures, but I know what they read when I set them and that becomes my baseline for checking.

I agree that relative pressures is what is important.

I try to get all 4 tires on my 5th wheel are the when cold and tires are not exposed to the sun.

Then when travelling if I see a tire that is more than 5 psi different than the others I find a tire shop or pull over in a safe place and examine the suspect tire very carefully.

On the truck I do the same for the front tires and the rear tires.

Those kinds of differences can be from a tire in the sun then not.

I have an expensive digital truck tire pressure monitor and my spares never see the sun shine as they are in an enclosed garage.....Both spares are brand new and the same brand.....

Not very practical if you need them on the road is it? :)

I guess I'm different in that I expect my TPMS to be accurate. And it is. It agrees with my tire pressure gauge/s and I would be unhappy with it if it didn't. If I had the issues the OP has I would be getting in touch with the company and have them replaced if they are in fact faulty.