diff --git a/index.html b/index.html
index 27c555e..a1ec414 100644
--- a/index.html
+++ b/index.html
@@ -152,7 +152,11 @@
                         Write changes permanently in the controller
                     </label>
 
-                    <br><br>
+                    <br>
+
+                    <p><small>Warning: <font color="red">Do not store the calibration permanently if
+                    the controller battery is low or disconnected. It will
+                    damage your controller.</font></small></p>
 
                     <p>Press <b>Start</b> to begin calibration.</p>