Petrus J.T.A. ("Piet") Battaerd spent his earliest years in Padang, on the island Sumatra, which was then part of the Dutch East Indies. At the age of 10 he went to the Netherlands where he completed his schooling. From 1901 to 1909 he studied medicine at the University of Leiden. During 1909-1910 he worked as assistant to the professor of physiology at Leiden, Willem Einthoven, who had developed the electrocardiograph a few years earlier, an achievement for which he received the Nobel Prize in medicine and physiology in 1924. Battaerd soon moved on to become assistant in the Department of Mental Diseases at Leiden (1911) and then to a similar position at the Mental Institution at Oegstgeest (1912-1913). During the latter year he qualified as Doctor of Medicine (MD) with a thesis titled Verdere graphische onderzoekingen over de acustische verschijnselen van het hart in normale en pathalogische omstandigheden (Further graphical investigations of the acoustic phenomena of the heart in normal and pathological circumstances; Leiden, 1913, 85 pp). A paper (in English) on this work was published in the journal Heart in 1915.
In October 1913 Battaerd was appointed as lecturer in physiology at the South African College, Cape Town (from 1918 the University of Cape Town). He came to South Africa at the invitation of Professor William A. Jolly*, who taught physiology at the college, and took up his post in 1914. He remained there to the end of 1920 and became known for his devoted attention and encouragement to his many medical students. During these years he worked closely with Professor Jolly on electrocardiography. He also acted as an examiner in physiology for the University of the Cape of Good Hope during the examinations of 1915/6 and 1916/7. By 1917 he was a member of the Royal Society of South Africa.
In 1921 Battaerd left Cape Town to become professor of physiology at the University of Stellenbosch from the 1st of March. He stayed in this post to his death in 1948. His first students reached the MSc level in 1926.
Battaerd was a friendly and popular person who excelled in his hobbies of weaving, cooking and carpentry. In 1916 he married Marguerite Koch, with whom he had a son. After her death he married Susan de Villiers in 1937.