His Illustrious Highness Count Louis (Ludwig) Alexander of Battenberg was born in Graz, Austria, the eldest son of Prince Alexander of Hesse and by Rhine (1823-1888) by his morganatic marriage to Julie Therese née Countess von Hauke (1825-1895), the daughter of a Polish politician. His mother was created Countess of Battenberg with the style Illustrious Highness on marriage. She was created Princess of Battenberg with the style of Serene Highness by her brother-in-law, Grand Duke Ludwig III of Hesse and by Rhine on 21 December 1858. Thereupon, Count Louis became HSH Prince Louis of Battenberg. One his younger brothers, Prince Alexander of Battenberg (1857-1893), became the reigning Prince of Bulgaria from 1879 to 1886, and another, Prince Henry of Battenberg (1858-1896), married Princess Beatrice of Great Britain and Ireland, the youngest child of Queen Victoria and Prince Albert of Saxe-Coburg-Gotha.
In 1868, at the age of fourteen, Prince Louis became a naturalized British subject and joined the Royal Navy. He began his career as a midshipman on the Royal Alfred. In 1876, he accompanied the Prince of Wales, the future King Edward VII on his official tour of India. During the 1882 Egyptian intervention, he served as a lieutenant on Inconstant and was decorated with the Egyptian Medal and the Khedive Bronze Star. In September 1883, Queen Victoria appointed him lieutenant in her yacht, Victoria and Albert, which assured his promotion to commander two years later. Prince Louis rose to the rank of captain and became an aide-de-camp to the Queen in 1891. He was promoted to rear admiral in 1904, vice admiral in 1910, and admiral in 1912. During that time, he served as Director of Naval Intelligence (1902-1905), Commander-in-Chief of the Atlantic Fleet (1908-1911), commander of the Third and Fourth Divisions of the Home Fleet (1911), and Second Sea Lord (1911). He became a Knight Commander of the Order of the Bath (K.C.B.) in the military division in 1908, having received the K.C.B. and Knight Grand Cross (G.C.B.) in the civil division of the same order in 1884 and 1887, respectively.
On 9 December 1912, Prince Louis assumed the post of First Sea Lord, the senior uniformed officer in the Royal Navy. In that capacity, he was responsible to the First Lord of the Admiralty (at the time, Winston Churchill) for the readiness of the fleet and the preparation of naval strategy. However, with the outbreak of World War I, rising anti-German sentiment among the British public and newspapers forced him to resign as First Sea Lord on 29 October 1914. He held no official post for the remainder of the war and retired from the active list in the Navy in 1918.
On 30 April 1884, Prince Louis of Battenberg married Princess Victoria of Hesse and by Rhine (5 April 1863-24 September 1950) at Darmstadt. His wife was the eldest daughter of Princess Alice of Great Britain and Ireland (26 April 1843-14 December 1878), the second daughter of Queen Victoria, and Grand Duke Ludwig VI of Hesse and by Rhine (12 September 1837-13 March 1892). Prince and Princess Louis of Battenberg were first cousins once removed; his father-in-law was also his first cousin. The marriage produced four children 1:
The Marquess of Miford Haven was appointed a member of the Privy Council and was promoted to the rank of Admiral of the Fleet in recognition of his service to the Royal Navy in August 1921. He died in London on 11 September 1921. His remains were buried at Whippingham Church on the Isle of Wight.
2 Upon relinquishing his princely title and Anglicizing his surname to Mountbatten, Prince Louis allegedly wrote in a letter to his son George, "Enter Prince Jeckel, exit Lord Hyde."