Battery level accuracy on sensors

One of my motion sensors went dead last month. I tried re-seating the battery a few times and pressing the reset button, but it didn’t do anything and no led flashed on.
The smart things app said the last known battery level was about 56%, but I bought a pack of new batteries and now it’s working straight away again on a new one.

I guess the indicated battery level is highly inaccurate?
Is 6 months typical battery life?

Battery levels is a hit or miss, the topic is discussed a lot. As for the six months it all depends on conditions of the sensor.

Everyone of my SmartSense Motion sensors stopped working at 78% battery. So the reading of batteries is way off.

I concur, all my sensors are pretty accurate down to failing < 10% but the new ST motion dies at 60-70% and give no indication except failure to work.
I have RBoys battery monitor set up with a special rule just for ST motions so I can catch them at this deceiving level.