I have 4 Shelly H&T in my home and wanted to update the firmware on all of them. I had to replace the battery in 3 of them (now active for 13 months). After I changed the batteries the 4 devices were reporting 41% and 100% of course. After I updated the firmware the one device reports 0% and the other 3 devices report 65%.
So did you break the battery level measurement, since even the one on 0% keeps reporting its state to MQTT.
It updated to the latest version, didn't check for the version number because I don't want to risk losing another 40% of my battery. 
