diff --git a/Documentation/pycardium/os.rst b/Documentation/pycardium/os.rst
index 7f76828331450f33f4d0494b0ac30093d7ca8280..e7e174ca3dc7b27dad5746f6bce86782b76f6bc8 100644
--- a/Documentation/pycardium/os.rst
+++ b/Documentation/pycardium/os.rst
@@ -53,6 +53,15 @@ Card10-Specific
    :param str name: Path to new app/script/l0dable.
    :return: This function never returns.  It can, however raise an exception.
 
+.. py:function:: read_battery()
+
+   Read the current battery voltage in V.  Please keep in mind that battery
+   voltage behaves exponentially when interpreting this value.
+
+   .. warning::
+
+      Card10 will hard-shutdown once the voltage drops below 3.4 V
+
 .. py:function:: reset()
 
    Reboot card10.