diff --git a/offchain/concurrency.py b/offchain/concurrency.py
index 1cc4c03..9597612 100644
--- a/offchain/concurrency.py
+++ b/offchain/concurrency.py
@@ -1,9 +1,12 @@
 import multiprocessing
 from concurrent.futures import ThreadPoolExecutor
-from typing import Any, Callable, Sequence
+from typing import Any, Callable, Sequence, TypeVar
 
 from offchain.logger.logging import logger
 
+T = TypeVar("T")
+U = TypeVar("U")
+
 MAX_PROCS = (multiprocessing.cpu_count() * 2) + 1
 
 
@@ -39,15 +42,11 @@ def parmap(fn: Callable, args: list) -> list:  # type: ignore[type-arg]
     return list(parallelize_with_threads(*map(lambda i: lambda: fn(i), args)))  # type: ignore[arg-type]  # noqa: E501
 
 
-def batched_parmap(fn: Callable, args: list, batch_size: int = 10) -> list:  # type: ignore[type-arg]  # noqa: E501
+def batched_parmap(fn: Callable[[T], U], args: list[T], batch_size: int = 10) -> list[U]:  # noqa: E501
     results = []
-    i, j = 0, 0
-    while i < len(args):
-        i, j = i + batch_size, i
-        if len(args) > i:
-            batch = args[j:i]
-        else:
-            batch = args[j:]
+    for i in range(0, len(args), batch_size):
+        batch_end = i + batch_size
+        batch = args[i:batch_end]
         res = parmap(fn, batch)
-        results += res
+        results.extend(res)
     return results
diff --git a/tests/test_concurrency.py b/tests/test_concurrency.py
new file mode 100644
index 0000000..87b2567
--- /dev/null
+++ b/tests/test_concurrency.py
@@ -0,0 +1,14 @@
+import pytest
+
+from offchain.concurrency import batched_parmap
+
+
+@pytest.mark.parametrize("batch_size", range(1, 11))
+def test_batched_parmap(batch_size):
+    def square(x):
+        return x * x
+
+    args = list(range(0, 10))
+    expected = [square(x) for x in args]
+    result = batched_parmap(square, args, batch_size=batch_size)
+    assert result == expected