I use Homematic (German Brand) thermostats, battery based RF885mhz and have very good experience (11 Units so far for around 4 years i paIed 29€ as a kit - no soldering only the manual finishes to be done)
demo table with the data acquisition you can find here:
2 years on 2xAA batteries. These reduced my heating costs about 30% and I managed to program them with a nice UI on the original dashboard to get a good acceptance factor from my family) I use them together with window sensors from the same brand. They talk together directly also the thermostats when you have more than one per room are directly synchronized without the Not so perfect but working hub called ccu. Even two in an outside building have good reception.
