To protect the batteries from damage whilst the train is running, the battery chambers were sealed with a 44 inches door, which was originally designed in use on the similar Class 42 to lock in position whilst the train was running via carriage-locks that would be activated by a square-key, but the Class 52 had an additional feature in the form of a pear-shaped metal catch known as the "Pear-drop" that would catch the battery box door in case the carriage-locks failed to engage, which had happened on the Class 42 before.