@Necessiter It's not understandable but this 'trick' helped me as well. I also put in new batteries yesterday but the Kasa app showed me only 75% battery. After doing what you did Kasa showed 100% battery 

  @Wayne-TP 

 sorry for late response,

 no,  the last was connected to the radiator while in pairing process. that's why low bat was shown after registration.

Rest was paired aside from radiator, than mounted to rad. and then I issued calibration proc of the valve.

this way works for all with correct batt status after the installation

thanks.