diff --git a/googleapiclient/discovery.py b/googleapiclient/discovery.py
index f7bbd77763c..faacfc5f07e 100644
--- a/googleapiclient/discovery.py
+++ b/googleapiclient/discovery.py
@@ -586,6 +586,8 @@ def build_from_document(
 
     schema = Schemas(service)
 
+    is_mtls = False
+
     # If the http client is not specified, then we must construct an http client
     # to make requests. If the service has scopes, then we also need to setup
     # authentication.
@@ -685,36 +687,38 @@ def build_from_document(
             )
             http_channel.add_certificate(key_path, cert_path, "", passphrase)
 
-        # If user doesn't provide api endpoint via client options, decide which
-        # api endpoint to use.
-        if "mtlsRootUrl" in service and (
-            not client_options or not client_options.api_endpoint
-        ):
-            mtls_endpoint = urllib.parse.urljoin(
-                service["mtlsRootUrl"], service["servicePath"]
-            )
-            use_mtls_endpoint = os.getenv(GOOGLE_API_USE_MTLS_ENDPOINT, "auto")
-
-            if not use_mtls_endpoint in ("never", "auto", "always"):
-                raise MutualTLSChannelError(
-                    "Unsupported GOOGLE_API_USE_MTLS_ENDPOINT value. Accepted values: never, auto, always"
-                )
-
-            # Switch to mTLS endpoint, if environment variable is "always", or
-            # environment varibable is "auto" and client cert exists.
-            if use_mtls_endpoint == "always" or (
-                use_mtls_endpoint == "auto" and client_cert_to_use
-            ):
-                if HAS_UNIVERSE and universe_domain != universe.DEFAULT_UNIVERSE:
-                    raise MutualTLSChannelError(
-                        f"mTLS is not supported in any universe other than {universe.DEFAULT_UNIVERSE}."
-                    )
-                base = mtls_endpoint
     else:
         # Check google-api-core >= 2.18.0 if credentials' universe != "googleapis.com".
         http_credentials = getattr(http, "credentials", None)
         _check_api_core_compatible_with_credentials_universe(http_credentials)
 
+    # If user doesn't provide api endpoint via client options, decide which
+    # api endpoint to use.
+    if "mtlsRootUrl" in service and (
+        not client_options or not client_options.api_endpoint
+    ):
+        mtls_endpoint = urllib.parse.urljoin(
+            service["mtlsRootUrl"], service["servicePath"]
+        )
+        use_mtls_endpoint = os.getenv(GOOGLE_API_USE_MTLS_ENDPOINT, "auto")
+
+        if not use_mtls_endpoint in ("never", "auto", "always"):
+            raise MutualTLSChannelError(
+                "Unsupported GOOGLE_API_USE_MTLS_ENDPOINT value. Accepted values: never, auto, always"
+            )
+
+        # Switch to mTLS endpoint, if environment variable is "always", or
+        # environment varibable is "auto" and client cert exists.
+        if use_mtls_endpoint == "always" or (
+            use_mtls_endpoint == "auto" and client_cert_to_use
+        ):
+            if HAS_UNIVERSE and universe_domain != universe.DEFAULT_UNIVERSE:
+                raise MutualTLSChannelError(
+                    f"mTLS is not supported in any universe other than {universe.DEFAULT_UNIVERSE}."
+                )
+            base = mtls_endpoint
+            is_mtls = True
+
     if model is None:
         features = service.get("features", [])
         model = JsonModel("dataWrapper" in features)
@@ -729,6 +733,7 @@ def build_from_document(
         rootDesc=service,
         schema=schema,
         universe_domain=universe_domain,
+        is_mtls=is_mtls
     )
 
 
@@ -1406,6 +1411,7 @@ def __init__(
         rootDesc,
         schema,
         universe_domain=universe.DEFAULT_UNIVERSE if HAS_UNIVERSE else "",
+        is_mtls=False
     ):
         """Build a Resource from the API description.
 
@@ -1438,6 +1444,7 @@ def __init__(
         self._schema = schema
         self._universe_domain = universe_domain
         self._credentials_validated = False
+        self.is_mtls = is_mtls
 
         self._set_service_methods()
 
@@ -1494,8 +1501,12 @@ def _set_service_methods(self):
     def _add_basic_methods(self, resourceDesc, rootDesc, schema):
         # If this is the root Resource, add a new_batch_http_request() method.
         if resourceDesc == rootDesc:
+            if self.is_mtls and "mtlsRootUrl" in rootDesc:
+                root_url = rootDesc["mtlsRootUrl"]
+            else:
+                root_url = rootDesc["rootUrl"]
             batch_uri = "%s%s" % (
-                rootDesc["rootUrl"],
+                root_url,
                 rootDesc.get("batchPath", "batch"),
             )