The batteries used in Samsung Electronics Co.’s troubled Galaxy Note 7 were tested by a lab that belongs to the South Korean electronics giant, a practice that sets it apart from other smartphone manufacturers.

To sell smartphones at major U.S. carriers, phone makers are required to test phone batteries at one of the 28 labs certified by the U.S. wireless industry’s trade group, the CTIA, to ensure compliance with standards set by the Institute of Electrical and Electronics Engineers.

Samsung...