All my Ikea stuff is using rechargeable batteries. My older motion sensors have dropped 10% each in six months (54 to 45, 49 to 39).

So with regular batteries, you might well not notice much drop though I would have expected a few percent given they seem to be calibrated to non-rechargeable batteries.

I would check that the battery number has actually updated with the "minutes ago" field. I had the air quality sensor intermittently disconnect and not report only some of it's metrics but Home Assistant seemed to keep displaying a flat line regardless (if I recall correctly).