Bosch PIR Motion Detector Battery Status

I have several Bosch motion doctors that work great. But battery always shows 100%. Consequently I never realize when the battery needs replacing unless I noticed one not working. Anyone have any suggestions as to how to check this?

I am curious what model you have. I recently installed a couple ISW-ZDL1-WP11G. It will be good to learn if battery percentage reporting is skewed.

Mine are the ISW-ZPR1-WP13. I'm guessing they don't report battery level even tho the level is shown on the device page. But it's always 100.

Is there anything that can be gleaned from the State Variable "lastBattery"?

A quick search did not provide any info to decipher this variable. I would love to get raw voltage data versus a percentage of unknown calculation. These are running on 6xAA, so not only a higher voltage, but also alkaline chemistry that will have a very different discharge curve than sensors with 3V lithium.