diff --git a/CHANGELOG.md b/CHANGELOG.md
index c7800b170b..d03f110677 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- Error when loading a previously run `Batch` or `ComponentModeler` containing custom data.
+
 ## [2.7.1]
 
 ### Added
diff --git a/tidy3d/plugins/smatrix/component_modelers/base.py b/tidy3d/plugins/smatrix/component_modelers/base.py
index 295ab4b050..973261a531 100644
--- a/tidy3d/plugins/smatrix/component_modelers/base.py
+++ b/tidy3d/plugins/smatrix/component_modelers/base.py
@@ -2,7 +2,6 @@
 
 from __future__ import annotations
 
-import json
 import os
 from abc import ABC, abstractmethod
 from typing import Dict, Tuple, Union
@@ -120,19 +119,9 @@ def _task_name(port: Port, mode_index: int = None) -> str:
     def sim_dict(self) -> Dict[str, Simulation]:
         """Generate all the :class:`Simulation` objects for the S matrix calculation."""
 
-    def json(self, **kwargs):
-        """Save component to dictionary. Add the ``batch`` if it has been cached."""
-
-        self_json = super().json(**kwargs)
-
-        batch = self._cached_properties.get("batch")
-
-        if not batch:
-            return self_json
-
-        self_dict = json.loads(self_json)
-        self_dict["batch_cached"] = json.loads(batch.json())
-        return json.dumps(self_dict)
+    def to_file(self, *args, **kwargs):
+        new_self = self.updated_copy(batch_cached=self.batch)
+        super(AbstractComponentModeler, new_self).to_file(*args, **kwargs)
 
     @cached_property
     def batch(self) -> Batch:
@@ -180,7 +169,7 @@ def get_path_dir(self, path_dir: str) -> None:
     @cached_property
     def _batch_path(self) -> str:
         """Where we store the batch for this ComponentModeler instance after the run."""
-        return os.path.join(self.path_dir, "batch" + str(hash(self)) + ".json")
+        return os.path.join(self.path_dir, "batch" + str(hash(self)) + ".hdf5")
 
     def _run_sims(self, path_dir: str = DEFAULT_DATA_DIR) -> BatchData:
         """Run :class:`Simulations` for each port and return the batch after saving."""
diff --git a/tidy3d/web/api/container.py b/tidy3d/web/api/container.py
index 8fd94d3d9e..c3e45e33b6 100644
--- a/tidy3d/web/api/container.py
+++ b/tidy3d/web/api/container.py
@@ -3,7 +3,6 @@
 from __future__ import annotations
 
 import concurrent
-import json
 import os
 import time
 from abc import ABC
@@ -171,19 +170,9 @@ class Job(WebContainer):
         "parent_tasks",
     )
 
-    def json(self, **kwargs):
-        """Save ``Job`` to dictionary. Add the `task_id` if it has been cached."""
-
-        self_json = super().json(**kwargs)
-
-        task_id = self._cached_properties.get("task_id")
-
-        if not task_id:
-            return self_json
-
-        self_dict = json.loads(self_json)
-        self_dict["task_id_cached"] = task_id
-        return json.dumps(self_dict)
+    def to_file(self, *args, **kwargs):
+        new_self = self.updated_copy(task_id_cached=self.task_id)
+        super(Job, new_self).to_file(*args, **kwargs)
 
     def run(self, path: str = DEFAULT_DATA_PATH) -> SimulationDataType:
         """Run :class:`Job` all the way through and return data.
@@ -587,19 +576,9 @@ def jobs(self) -> Dict[TaskName, Job]:
             jobs[task_name] = job
         return jobs
 
-    def json(self, **kwargs):
-        """Save ``Batch`` to dictionary. Add the ``jobs`` if they have been cached."""
-
-        self_json = super().json(**kwargs)
-
-        jobs = self._cached_properties.get("jobs")
-
-        if not jobs:
-            return self_json
-
-        self_dict = json.loads(self_json)
-        self_dict["jobs_cached"] = {k: json.loads(j.json()) for k, j in jobs.items()}
-        return json.dumps(self_dict)
+    def to_file(self, *args, **kwargs):
+        new_self = self.updated_copy(jobs_cached=self.jobs)
+        super(Batch, new_self).to_file(*args, **kwargs)
 
     @property
     def num_jobs(self) -> int: