Which version of OH2 with which version of the Z-Wave binding are you using?
You can also use the following in your Item definition:
Number fire_alarm_com_bat "Fire Alarm Sensor Battery Level: [%d %%]" <battery> (all_batteries) {channel="zwave:device:512:node34:battery-level"}
I updated https://www.cd-jackson.com/index.php/zwave/zwave-device-database/zwave-device-list/devicesummary/817