diff --git a/lerobot/common/datasets/abstract.py b/lerobot/common/datasets/abstract.py
index 34b33c2e6..5db97497a 100644
--- a/lerobot/common/datasets/abstract.py
+++ b/lerobot/common/datasets/abstract.py
@@ -49,9 +49,9 @@ def __init__(
     @property
     def stats_patterns(self) -> dict:
         return {
-            ("observation", "state"): "b c -> 1 c",
-            ("observation", "image"): "b c h w -> 1 c 1 1",
-            ("action",): "b c -> 1 c",
+            ("observation", "state"): "b c -> c",
+            ("observation", "image"): "b c h w -> c",
+            ("action",): "b c -> c",
         }
 
     @property
diff --git a/lerobot/common/datasets/aloha.py b/lerobot/common/datasets/aloha.py
index 52a5676ee..0637f8a37 100644
--- a/lerobot/common/datasets/aloha.py
+++ b/lerobot/common/datasets/aloha.py
@@ -113,11 +113,11 @@ def __init__(
     @property
     def stats_patterns(self) -> dict:
         d = {
-            ("observation", "state"): "b c -> 1 c",
-            ("action",): "b c -> 1 c",
+            ("observation", "state"): "b c -> c",
+            ("action",): "b c -> c",
         }
         for cam in CAMERAS[self.dataset_id]:
-            d[("observation", "image", cam)] = "b c h w -> 1 c 1 1"
+            d[("observation", "image", cam)] = "b c h w -> c"
         return d
 
     @property
diff --git a/lerobot/common/envs/factory.py b/lerobot/common/envs/factory.py
index d6b294ebe..de86b3ad8 100644
--- a/lerobot/common/envs/factory.py
+++ b/lerobot/common/envs/factory.py
@@ -1,17 +1,31 @@
 from torchrl.envs.transforms import Compose, StepCounter, Transform, TransformedEnv
 
 
-def make_env(cfg, seed=None, transform=None):
+def make_env(cfg, transform=None):
     """
     Provide seed to override the seed in the cfg (useful for batched environments).
     """
+    # assert cfg.rollout_batch_size == 1, \
+    # """
+    # For the time being, rollout batch sizes of > 1 are not supported. This is because the SerialEnv rollout does not
+    # correctly handle terminated environments. If you really want to use a larger batch size, read on...
+
+    # When calling `EnvBase.rollout` with `break_when_any_done == True` all environments stop rolling out as soon as the
+    # first is terminated or truncated. This almost certainly results in incorrect success metrics, as all but the first
+    # environment get an opportunity to reach the goal. A possible work around is to comment out `if any_done: break`
+    # inf `EnvBase._rollout_stop_early`. One potential downside is that the environments `step` function will continue
+    # to be called and the outputs will continue to be added to the rollout.
+
+    # When calling `EnvBase.rollout` with `break_when_any_done == False` environments are reset when done.
+    # """
+
     kwargs = {
         "frame_skip": cfg.env.action_repeat,
         "from_pixels": cfg.env.from_pixels,
         "pixels_only": cfg.env.pixels_only,
         "image_size": cfg.env.image_size,
         "num_prev_obs": cfg.n_obs_steps - 1,
-        "seed": seed if seed is not None else cfg.seed,
+        "seed": cfg.seed,
     }
 
     if cfg.env.name == "simxarm":
@@ -33,22 +47,33 @@ def make_env(cfg, seed=None, transform=None):
     else:
         raise ValueError(cfg.env.name)
 
-    env = clsfunc(**kwargs)
+    def _make_env(seed):
+        nonlocal kwargs
+        kwargs["seed"] = seed
+        env = clsfunc(**kwargs)
+
+        # limit rollout to max_steps
+        env = TransformedEnv(env, StepCounter(max_steps=cfg.env.episode_length))
 
-    # limit rollout to max_steps
-    env = TransformedEnv(env, StepCounter(max_steps=cfg.env.episode_length))
+        if transform is not None:
+            # useful to add normalization
+            if isinstance(transform, Compose):
+                for tf in transform:
+                    env.append_transform(tf.clone())
+            elif isinstance(transform, Transform):
+                env.append_transform(transform.clone())
+            else:
+                raise NotImplementedError()
 
-    if transform is not None:
-        # useful to add normalization
-        if isinstance(transform, Compose):
-            for tf in transform:
-                env.append_transform(tf.clone())
-        elif isinstance(transform, Transform):
-            env.append_transform(transform.clone())
-        else:
-            raise NotImplementedError()
+        return env
 
-    return env
+    # return SerialEnv(
+    #     cfg.rollout_batch_size,
+    #     create_env_fn=_make_env,
+    #     create_env_kwargs={
+    #         "seed": env_seed for env_seed in range(cfg.seed, cfg.seed + cfg.rollout_batch_size)
+    #     },
+    # )
 
 
 # def make_env(env_name, frame_skip, device, is_test=False):
diff --git a/lerobot/common/policies/abstract.py b/lerobot/common/policies/abstract.py
index 9c652c0a3..ca2d8570a 100644
--- a/lerobot/common/policies/abstract.py
+++ b/lerobot/common/policies/abstract.py
@@ -30,7 +30,7 @@ def select_action(self, observation) -> Tensor:
         Should return a (batch_size, n_action_steps, *) tensor of actions.
         """
 
-    def forward(self, *args, **kwargs):
+    def forward(self, *args, **kwargs) -> Tensor:
         """Inference step that makes multi-step policies compatible with their single-step environments.
 
         WARNING: In general, this should not be overriden.
diff --git a/lerobot/configs/default.yaml b/lerobot/configs/default.yaml
index 5cc8acd24..27b75c88d 100644
--- a/lerobot/configs/default.yaml
+++ b/lerobot/configs/default.yaml
@@ -11,14 +11,16 @@ hydra:
 
 seed: 1337
 # batch size for TorchRL SerialEnv. Each underlying env will get the seed = seed + env_index
-rollout_batch_size: 10
+# NOTE: batch size of 1 is not yet supported! This is just a placeholder for future support. See
+# `lerobot.common.envs.factory.make_env` for more information.
+rollout_batch_size: 1
 device: cuda  # cpu
 prefetch: 4
 eval_freq: ???
 save_freq: ???
 eval_episodes: ???
 save_video: false
-save_model: false
+save_model: true
 save_buffer: false
 train_steps: ???
 fps: ???
@@ -31,7 +33,7 @@ env: ???
 policy: ???
 
 wandb:
-  enable: true
+  enable: false
   # Set to true to disable saving an artifact despite save_model == True
   disable_artifact: false
   project: lerobot
diff --git a/lerobot/configs/policy/diffusion.yaml b/lerobot/configs/policy/diffusion.yaml
index 0dae5056d..ce8acbd47 100644
--- a/lerobot/configs/policy/diffusion.yaml
+++ b/lerobot/configs/policy/diffusion.yaml
@@ -22,8 +22,8 @@ keypoint_visible_rate: 1.0
 obs_as_global_cond: True
 
 eval_episodes: 1
-eval_freq: 10000
-save_freq: 100000
+eval_freq: 5000
+save_freq: 5000
 log_freq: 250
 
 offline_steps: 1344000
diff --git a/lerobot/scripts/eval.py b/lerobot/scripts/eval.py
index 7cfb796af..c0199c0c4 100644
--- a/lerobot/scripts/eval.py
+++ b/lerobot/scripts/eval.py
@@ -9,7 +9,7 @@
 import torch
 import tqdm
 from tensordict.nn import TensorDictModule
-from torchrl.envs import EnvBase, SerialEnv
+from torchrl.envs import EnvBase
 from torchrl.envs.batched_envs import BatchedEnvBase
 
 from lerobot.common.datasets.factory import make_offline_buffer
@@ -131,14 +131,7 @@ def eval(cfg: dict, out_dir=None):
     offline_buffer = make_offline_buffer(cfg)
 
     logging.info("make_env")
-    env = SerialEnv(
-        cfg.rollout_batch_size,
-        create_env_fn=make_env,
-        create_env_kwargs=[
-            {"cfg": cfg, "seed": env_seed, "transform": offline_buffer.transform}
-            for env_seed in range(cfg.seed, cfg.seed + cfg.rollout_batch_size)
-        ],
-    )
+    env = make_env(cfg, transform=offline_buffer.transform)
 
     if cfg.policy.pretrained_model_path:
         policy = make_policy(cfg)
diff --git a/lerobot/scripts/train.py b/lerobot/scripts/train.py
index 2c7bb5751..5ecd616d4 100644
--- a/lerobot/scripts/train.py
+++ b/lerobot/scripts/train.py
@@ -7,7 +7,6 @@
 from tensordict.nn import TensorDictModule
 from torchrl.data import LazyMemmapStorage, TensorDictReplayBuffer
 from torchrl.data.replay_buffers import PrioritizedSliceSampler
-from torchrl.envs import SerialEnv
 
 from lerobot.common.datasets.factory import make_offline_buffer
 from lerobot.common.envs.factory import make_env
@@ -149,14 +148,6 @@ def train(cfg: dict, out_dir=None, job_name=None):
 
     logging.info("make_env")
     env = make_env(cfg, transform=offline_buffer.transform)
-    env = SerialEnv(
-        cfg.rollout_batch_size,
-        create_env_fn=make_env,
-        create_env_kwargs=[
-            {"cfg": cfg, "seed": s, "transform": offline_buffer.transform}
-            for s in range(cfg.seed, cfg.seed + cfg.rollout_batch_size)
-        ],
-    )
 
     logging.info("make_policy")
     policy = make_policy(cfg)
diff --git a/tests/data/aloha_sim_insertion_human/stats.pth b/tests/data/aloha_sim_insertion_human/stats.pth
index 869d26cd0..f909ed075 100644
Binary files a/tests/data/aloha_sim_insertion_human/stats.pth and b/tests/data/aloha_sim_insertion_human/stats.pth differ
diff --git a/tests/data/pusht/stats.pth b/tests/data/pusht/stats.pth
index 037e02f0f..8846b8f65 100644
Binary files a/tests/data/pusht/stats.pth and b/tests/data/pusht/stats.pth differ
diff --git a/tests/test_policies.py b/tests/test_policies.py
index 92324485d..ee5abdb79 100644
--- a/tests/test_policies.py
+++ b/tests/test_policies.py
@@ -1,4 +1,5 @@
 
+from omegaconf import open_dict
 import pytest
 from tensordict import TensorDict
 from tensordict.nn import TensorDictModule
@@ -7,7 +8,8 @@
 from torchrl.envs import EnvBase
 
 from lerobot.common.policies.factory import make_policy
-
+from lerobot.common.envs.factory import make_env
+from lerobot.common.datasets.factory import make_offline_buffer
 from lerobot.common.policies.abstract import AbstractPolicy
 
 from .utils import DEVICE, init_config
@@ -30,7 +32,19 @@ def test_factory(env_name, policy_name):
             f"device={DEVICE}",
         ]
     )
+    # Check that we can make the policy object.
     policy = make_policy(cfg)
+    # Check that we run select_action and get the appropriate output.
+    if env_name == "simxarm":
+        # TODO(rcadene): Not implemented
+        return
+    if policy_name == "tdmpc":
+        # TODO(alexander-soare): TDMPC does not use n_obs_steps but the environment requires this.
+        with open_dict(cfg):
+            cfg['n_obs_steps'] = 1
+    offline_buffer = make_offline_buffer(cfg)
+    env = make_env(cfg, transform=offline_buffer.transform)
+    policy.select_action(env.observation_spec.rand()['observation'].to(DEVICE), torch.tensor(0, device=DEVICE))
 
 
 def test_abstract_policy_forward():