Have you woken up the device? Some battery devices need to be woken up multiple times before they’re fully discovered. If after that it’s still showing Unknown, can you check for the existence of a “node.xml” file for that node in the userdata/zwave directory? If the file is there, please post the manufacturer, deviceId, and deviceType. It will look something like this, but with numbers specific to your device.
<manufacturer>0x1d</manufacturer>
<deviceId>0x206</deviceId>
<deviceType>0x201</deviceType>
Also, what version of openHAB are you running? If you’re on the 2.3 release, which is very old at this point, the database possibly didn’t contain this device when 2.3 was built.