diff --git a/README.md b/README.md
index da3240f..b51a389 100644
--- a/README.md
+++ b/README.md
@@ -43,3 +43,10 @@ you'll need a browser which supports webGL (e.g. chromium).
   - call with `--render-phone` to see how the phone would fit inside the case, or apply any of the environment variables from above.
 
 - CadQuery docs may be found here: <https://cadquery.readthedocs.io/en/latest/quickstart.html>
+
+
+## Bill of Materials
+- print using a flexible material like TPU
+- the "ldtek" battery is sold under a few brands:
+  - [Auskang](https://www.amazon.com/Auskang-Portable-5000mAh-Compatible-Android/dp/B093GKX5Z1)
+  - [TNTOR](https://www.amazon.com/TNTOR-Portable-Charger-5000mAh-Compatible/dp/B0C3QH7RYK/)
diff --git a/src/ldtek_battery.py b/src/ldtek_battery.py
index 0f28575..0d29a0f 100644
--- a/src/ldtek_battery.py
+++ b/src/ldtek_battery.py
@@ -1,3 +1,7 @@
+# this battery sells under a few brands.
+# - Auskang: <https://www.amazon.com/Auskang-Portable-5000mAh-Compatible-Android/dp/B093GKX5Z1>
+# - TNTOR: <https://www.amazon.com/TNTOR-Portable-Charger-5000mAh-Compatible/dp/B0C3QH7RYK/>
+# the manufacturer is listed as "Shenzen LDTEK Technology Co., Ltd"
 import cadquery as cq
 
 width = 65.6