Medieval battles were usually fairly short and decisive, due to the smaller sizes of forces involved and their relatively bloody nature. For example the battle of Agincourt was the culmination of a considerable campaign, but was over in about three hours. The defeated army would either be routed completely, or more likely would regroup with its remaining forces and retire, with the rear guard fighting a series of delaying actions until they can get enough distance between them and their pursuers. Battles rarely continued until everyone from one side was dead.

In cases where both sides either fight themselves to a stalemate or become too exhausted after a day's fighting that no side is either capable or desirous to press forward or retreat would return to camp and set up a watch to guard against a night attack. There are a lot of examples in antiquity (probably in medieval too but can't think specifically at the moment), where armies would camp near each other for many days on end, each day forming up 'to give battle', but one side or the other refusing to engage for whatever reason so they just returned to camp.

As /u/Rosstafarii points out, medieval battles (the actual engagements, that is) typically did not last for days at a time. Before battle was joined, raids, ambushes, and scouting parties might venture out at night and come into contact with the enemy, but a full-on nighttime assault would be rare. Commanding large bodies of men was difficult enough during the day. Ordering a full advance at night would be even more difficult and introduce new problems. Troops would not be able to see banners (or where they were going), which could lead to uncoordinated attacks that could be isolated and defeated in detail.

A reply to /u/Abels_Angel

I was wondering for authenticity.

Are you by chance writing a historical fiction? ;-)

This isn't a naive nor amateurish question, but one that is hard to answer because you are asking for "what is typical" and the best answer is that there is nothing typical about what happened at night during battles.

But as a starting point, I recommend that you look into several battles through which you can learn the means and ways of conducting battles. In the Battle of Crécy (1346) during the earliest phase of the Hundred Years War, the army of Philip VI of France encountered the English army of Edward III late in the day, and the battle lasted through the night even though it became more a series of skirmishes.

I like The Hundred Years War: The English in France 1337-1453 by Desmond Seward, however this battle is well-studied and there are other sources too.