I saw at least one brand that used small batteries. Geez, the $37 (!) option uses solar for the readout on the dash, and lithium coins for hte sensors.

https://www.amazon.com/Favoto-Monitoring-Universal-Real-time-Temperature/dp/B078RD479X/ref=lp_2201765011_1_7?s=automotive&ie=UTF8&qid=1582045434&sr=1-7

Geez, at that price almost cheap as the tire caps I always lose when airing down :)