Voltaire is said to have drunk 40-50 cups of coffee a day.
Elsewhere, from Did Voltaire really drink 40 to 50 cups of coffee a day? Stephen G. Tallentyre (which is the pen name of Evelyn Beatrice Hall) wrote that:
He dined in Paris that night at a coffee-house, with a few other literary men. He arrived rather late. He had come straight from Versailles, and alone of the company knew what had occurred there. He made his dinner, after his frugal fashion, off seven or eight cups of black coffee and a couple of rolls, and was very talkative and amusing.”
Stephen G. Tallentyre, The Life of Voltaire (1903)
But this says only about dinner, and not the whole day.
From Cincinnati Lancet and Clinic, p. 15.
“[T]he philosopher took as high as fifty cups on some days. This would perhaps explain the nobility of Voltaire’s mind and its sudden bursts of enthusiasm, for, according to Condorcet (Vie de Voltaire) he passed in an instant from wrath to tenderness, from violent indignation to sunny pleasantness.”
Here it says 50 cups.