The valve stem sensors have lithium batteries in them. Will they work in colder temps?? If not will they start to work if a heating issue were to develope?? Of course maybe that would be to late anyhow.
I think you will be fine. They are not putting out max amps to power the sensors. From what I read on battery university's site at 0 degrees an Li battery losses 50% of it's capacity due to increased resistance. If your batteries are to last 8 years or more in your sensors what percentage of the available power do you think they actually need to operate?
