The "%" is simply the units. None of my battery powered devices show the units on the device detail page as shown above. So, I wouldn't worry too much about that.
However, I find it odd that there is no CONFIGURE button on that page. This makes we wonder if the Generic Z-Wave Smoke/CO Detector driver is sending configuration commands to the device at all? @mike.maxwell would know for sure and should be able to figure out what might be going on with this device/driver combination.
While waiting on an official Hubitat response, you might be able to manually configure the battery reporting settings of the device by using the following tool.
