Include unit in metric name

exporter.py

@@ -187,7 +187,7 @@ def __init__(self, ccu_host, ccu_port, auth, gathering_interval, reload_names_in
         # Upon request export the seconds since the last successful update.
         # This is robust against internal crashes and can be used by the healthcheck.
         self.refresh_time = time.time()
-        self.refresh_age = Gauge("refresh_age", "Seconds since the last successful refresh.", labelnames=["ccu"], namespace=self.METRICS_NAMESPACE)
+        self.refresh_age = Gauge("refresh_age_seconds", "Seconds since the last successful refresh.", labelnames=["ccu"], namespace=self.METRICS_NAMESPACE)
         self.refresh_age.labels(self.ccu_host).set_function(lambda: time.time() - self.refresh_time)
 
     def generate_metrics(self):