The Battle of Ballon took place on 22 November 845 between the forces of Charles the Bald, king of West Francia, and Nominoë, Duke of Brittany.

Following the death of Louis the Pious, Nominoë initially supported Charles the Bald in the dispute between him and his brothers over control of Frankish territory.

Learning of Charles's difficult military position in Toulouse, Nominoë continued his offensive, raiding Maine.

In November, he had intended to participate in a religious festival in Tours, but he decided to strike against Nominoë instead, having heard that a faction of discontented Bretons would defect to him if he hastened to their aid.

Nominoë lured the king into marshland at the confluence of the Oust and the Aff between Redon and Bains-sur-Oust, near Ballon Abbey - hence the name of the battle.

"[3] Following his defeat, rumors circulated that Charles had been killed, forcing him to make a quick public appearance in Maine.

In 1952 the battle was commemorated by the nationalist group Koun Breizh, who funded the erection of a statue of Nominoë by the artist Raffig Tullou in Bains-sur-Oust, near the site of the victory.