All Aqara window sensors suddenly read 100% battery...?

I have nine Aqara window sensors I use to turn thermostats on/off. They've been behaving erratically for the past few weeks, so yesterday I checked the battery status on one of them (can't remember which one) - steadily declining from >80% to around 35% now. Even showed the graph to my wife.
So I bought ten new batteries - they came today. Earlier today I updated HA Core and restarted. Now, all my Aqara window sensor batteries read 100% - even for the entire last month! All of them!
Can the Core update have messed with historical readings?