diff --git a/tianshou/data/batch.py b/tianshou/data/batch.py
index 04505ace3..03b3d9849 100644
--- a/tianshou/data/batch.py
+++ b/tianshou/data/batch.py
@@ -190,7 +190,7 @@ def alloc_by_keys_diff(
         if key in meta.get_keys():
             if isinstance(meta[key], Batch) and isinstance(batch[key], Batch):
                 alloc_by_keys_diff(meta[key], batch[key], size, stack)
-            elif isinstance(meta[key], Batch) and meta[key].is_empty():
+            elif isinstance(meta[key], Batch) and len(meta[key].get_keys()) == 0:
                 meta[key] = create_value(batch[key], size, stack)
         else:
             meta[key] = create_value(batch[key], size, stack)
@@ -768,7 +768,6 @@ def cat_(self, batches: BatchProtocol | Sequence[dict | BatchProtocol]) -> None:
                 if len(batch) > 0:
                     batch_list.append(Batch(batch))
             elif isinstance(batch, Batch):
-                # x.is_empty() means that x is Batch() and should be ignored
                 if len(batch.get_keys()) != 0:
                     batch_list.append(batch)
             else:
@@ -777,7 +776,7 @@ def cat_(self, batches: BatchProtocol | Sequence[dict | BatchProtocol]) -> None:
             return
         batches = batch_list
         try:
-            # x.is_empty(recurse=True) here means x is a nested empty batch
+            # len(batch) here means batch is a nested empty batch
             # like Batch(a=Batch), and we have to treat it as length zero and
             # keep it.
             lens = [0 if len(batch) == 0 else len(batch) for batch in batches]
@@ -806,7 +805,6 @@ def stack_(self, batches: Sequence[dict | BatchProtocol], axis: int = 0) -> None
                 if len(batch) > 0:
                     batch_list.append(Batch(batch))
             elif isinstance(batch, Batch):
-                # x.is_empty() means that x is Batch() and should be ignored
                 if len(batch.get_keys()) != 0:
                     batch_list.append(batch)
             else:
@@ -821,7 +819,7 @@ def stack_(self, batches: Sequence[dict | BatchProtocol], axis: int = 0) -> None
             {
                 batch_key
                 for batch_key, obj in batch.items()
-                if not (isinstance(obj, BatchProtocol) and obj.is_empty())
+                if not (isinstance(obj, BatchProtocol) and len(obj.get_keys()) == 0)
             }
             for batch in batches
         ]
@@ -867,7 +865,7 @@ def stack_(self, batches: Sequence[dict | BatchProtocol], axis: int = 0) -> None
                 # TODO: fix code/annotations s.t. the ignores can be removed
                 if (
                     isinstance(value, BatchProtocol)  # type: ignore
-                    and value.is_empty()  # type: ignore
+                    and len(value.get_keys()) == 0  # type: ignore
                 ):
                     continue  # type: ignore
                 try: