diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 0f5b13447..d51d0e135 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -37,6 +37,8 @@ Change Log
   this might cause an issue if you install `grid2op[chronix2grid]` for the short thermal
 - [BREAKING] force key-word arguments in `grid2op.make` except for the first one (env name), see
   [rte-france#503](https://github.com/rte-france/Grid2Op/issues/503)
+- [FIXED] a bug preventing to use storage units in "sim2real" environment (when the 
+  grid for forecast is not the same as the grid for the environment)
 - [ADDED] a CI to test package can be installed and loaded correctly on windows, macos and line_ex_to_sub_pos
   for python 3.8, 3.9, 3.10 and 3.11
 - [ADDED] possibility to change the "soft_overflow_threshold" in the parameters (like
diff --git a/grid2op/Observation/observationSpace.py b/grid2op/Observation/observationSpace.py
index db81a8991..afb2c919c 100644
--- a/grid2op/Observation/observationSpace.py
+++ b/grid2op/Observation/observationSpace.py
@@ -207,7 +207,7 @@ def _create_obs_env(self, env):
     def _aux_create_backend(self, env, observation_bk_class, observation_bk_kwargs, path_grid_for):
         if observation_bk_kwargs is None:
             observation_bk_kwargs = env.backend._my_kwargs
-        observation_bk_class_used = observation_bk_class.init_grid(env.backend)
+        observation_bk_class_used = observation_bk_class.init_grid(type(env.backend))
         self._backend_obs = observation_bk_class_used(**observation_bk_kwargs)   
         self._backend_obs.set_env_name(env.name)
         self._backend_obs.load_grid(path_grid_for)
diff --git a/grid2op/Space/GridObjects.py b/grid2op/Space/GridObjects.py
index 592528a1e..99bbfaa43 100644
--- a/grid2op/Space/GridObjects.py
+++ b/grid2op/Space/GridObjects.py
@@ -611,6 +611,9 @@ class GridObjects:
     alertable_line_names = []  # name of each line to produce an alert on # TODO
     alertable_line_ids = []
     
+    # test
+    _IS_INIT = False
+    
     def __init__(self):
         """nothing to do when an object of this class is created, the information is held by the class attributes"""
         pass
@@ -663,7 +666,7 @@ def _clear_class_attribute(cls):
         cls.attr_nan_list_set = set()
 
         # class been init
-        # __is_init = False
+        cls._IS_INIT = False
 
         # name of the objects
         cls.env_name = "unknown"
@@ -1255,8 +1258,9 @@ def _init_class_attr(self, obj=None):
             setattr(cls, attr_nm, attr)
 
     def _compute_pos_big_topo(self):
-        # TODO move the object attribute as class attribute !
-        self._init_class_attr()
+        # move the object attribute as class attribute !
+        if not type(self)._IS_INIT:
+            self._init_class_attr()
         cls = type(self)
         cls._compute_pos_big_topo_cls()
 
@@ -2702,7 +2706,9 @@ def init_grid(cls, gridobj, force=False, extra_name=None, force_module=None):
         else:
             # i am the original class from grid2op
             res_cls._INIT_GRID_CLS = cls
-
+        
+        res_cls._IS_INIT = True
+        
         res_cls._compute_pos_big_topo_cls()
         res_cls.process_shunt_satic_data()
         if res_cls.glop_version != grid2op.__version__: