diff --git a/sdk/python/feast/infra/online_stores/mysql_online_store/mysql.py b/sdk/python/feast/infra/online_stores/mysql_online_store/mysql.py
index 415184ea248..927e44db2b7 100644
--- a/sdk/python/feast/infra/online_stores/mysql_online_store/mysql.py
+++ b/sdk/python/feast/infra/online_stores/mysql_online_store/mysql.py
@@ -100,14 +100,14 @@ def online_write_batch(
                 if progress:
                     progress(1)
         else:
-            batch_size = config.online_store.bacth_size
+            batch_size = config.online_store.batch_size
             if not batch_size or batch_size < 2:
                 raise ValueError("Batch size must be at least 2")
             insert_values = []
             for entity_key, values, timestamp, created_ts in data:
                 entity_key_bin = serialize_entity_key(
                     entity_key,
-                    entity_key_serialization_version=2,
+                    entity_key_serialization_version=3,
                 ).hex()
                 timestamp = to_naive_utc(timestamp)
                 if created_ts is not None:
diff --git a/sdk/python/tests/unit/infra/online_store/test_mysql_online_store.py b/sdk/python/tests/unit/infra/online_store/test_mysql_online_store.py
new file mode 100644
index 00000000000..3a74f89c893
--- /dev/null
+++ b/sdk/python/tests/unit/infra/online_store/test_mysql_online_store.py
@@ -0,0 +1,107 @@
+"""Unit tests for the MySQL online store write paths (no live database)."""
+
+from datetime import datetime, timedelta, timezone
+from unittest.mock import MagicMock, patch
+
+from feast import Entity, FeatureView
+from feast.field import Field
+from feast.infra.online_stores.mysql_online_store.mysql import (
+    MySQLOnlineStore,
+    MySQLOnlineStoreConfig,
+)
+from feast.protos.feast.types.EntityKey_pb2 import EntityKey as EntityKeyProto
+from feast.protos.feast.types.Value_pb2 import Value as ValueProto
+from feast.repo_config import RepoConfig
+from feast.types import Float32, Int64
+from feast.value_type import ValueType
+
+
+def _make_feature_view(name: str = "driver_stats") -> FeatureView:
+    entity = Entity(
+        name="driver_id",
+        join_keys=["driver_id"],
+        value_type=ValueType.INT64,
+    )
+    return FeatureView(
+        name=name,
+        entities=[entity],
+        ttl=timedelta(days=1),
+        schema=[
+            Field(name="driver_id", dtype=Int64),
+            Field(name="trips_today", dtype=Int64),
+            Field(name="avg_rating", dtype=Float32),
+        ],
+    )
+
+
+def _make_entity_key(driver_id: int) -> EntityKeyProto:
+    entity_key = EntityKeyProto()
+    entity_key.join_keys.append("driver_id")
+    val = ValueProto()
+    val.int64_val = driver_id
+    entity_key.entity_values.append(val)
+    return entity_key
+
+
+def _repo_config(online_store_cfg: MySQLOnlineStoreConfig) -> RepoConfig:
+    return RepoConfig(
+        registry="dummy_registry.db",
+        project="test_project",
+        provider="local",
+        entity_key_serialization_version=3,
+        online_store=online_store_cfg,
+    )
+
+
+def _write_data(n: int) -> list:
+    now = datetime.now(tz=timezone.utc)
+    data = []
+    for i in range(n):
+        val = ValueProto()
+        val.int64_val = i
+        data.append((_make_entity_key(1000 + i), {"trips_today": val}, now, now))
+    return data
+
+
+class TestMySQLBatchWrite:
+    """The ``batch_write`` path of ``online_write_batch`` (no live database)."""
+
+    def test_batch_write_reads_batch_size_from_config(self):
+        """``batch_write`` must read the ``batch_size`` config field. It was
+        previously misspelled ``bacth_size``, which raised ``AttributeError`` on
+        the pydantic config and made the whole batch-write path unusable."""
+        store = MySQLOnlineStore()
+        config = _repo_config(
+            MySQLOnlineStoreConfig(type="mysql", batch_write=True, batch_size=2)
+        )
+        with (
+            patch.object(store, "_get_conn", return_value=MagicMock()),
+            patch.object(store, "_execute_batch") as mock_execute_batch,
+        ):
+            store.online_write_batch(config, _make_feature_view(), _write_data(3), None)
+
+        assert mock_execute_batch.called
+
+    def test_batch_write_uses_same_entity_key_version_as_read(self):
+        """The batch path must serialize entity keys with the same version the
+        single-row write path and ``online_read`` use (3), otherwise
+        batch-written rows cannot be read back."""
+        store = MySQLOnlineStore()
+        config = _repo_config(
+            MySQLOnlineStoreConfig(type="mysql", batch_write=True, batch_size=2)
+        )
+        with (
+            patch.object(store, "_get_conn", return_value=MagicMock()),
+            patch.object(store, "_execute_batch"),
+            patch(
+                "feast.infra.online_stores.mysql_online_store.mysql.serialize_entity_key",
+                return_value=b"\x00",
+            ) as mock_serialize,
+        ):
+            store.online_write_batch(config, _make_feature_view(), _write_data(2), None)
+
+        versions = {
+            call.kwargs["entity_key_serialization_version"]
+            for call in mock_serialize.call_args_list
+        }
+        assert versions == {3}
diff --git a/sdk/python/tests/universal/feature_repos/universal/online_store/mysql.py b/sdk/python/tests/universal/feature_repos/universal/online_store/mysql.py
index fa6978b259a..89320538c30 100644
--- a/sdk/python/tests/universal/feature_repos/universal/online_store/mysql.py
+++ b/sdk/python/tests/universal/feature_repos/universal/online_store/mysql.py
@@ -54,7 +54,7 @@ def create_online_store(self) -> Dict[str, str]:
             "database": "test",
             "port": exposed_port,
             "batch_write": "True",
-            "bacth_size": "1000",
+            "batch_size": "1000",
         }
 
     def teardown(self):