fixed render funciton and obsbuilder

marl_factory_grid/modules/batteries/entitites.py

@@ -49,9 +49,6 @@ class Battery(_Object):
         summary.update(dict(belongs_to=self._bound_entity.name, chargeLevel=self.charge_level))
         return summary
 
-    def render(self):
-        return None
-
 
 class Pod(Entity):
 

marl_factory_grid/modules/batteries/groups.py

@@ -23,6 +23,10 @@ class Batteries(Collection):
     def var_has_position(self):
         return False
 
+    @property
+    def var_can_be_bound(self):
+        return True
+
     @property
     def obs_tag(self):
         return self.__class__.__name__