Grenades were used by European, Muslims, and Chinese before 1800. However, there were no noticeable field-battle involving the hand grenades during the Napoleon era. One would imagine that grenades are effective against a square formation that is tight and slowly-moving. One or two grenades is enough to create a temporary disorder. Furthermore, the primary usage of grenades was to break tough defensive lines.
In early 1800, grenades are still frequently used in siege battle, and possibly in open battle:
The others are of the caliber of four, and weigh about two pounds. These last are called hand grenades, and are thrown into the covert way, or the trenches of a besieged place, or indeed into the midst of troops.
It is also documented that hand grenade were used during the Napoleonic era (1799−1815) and were used by both the French and British.
But why there is no documented battle in which hand-grenades play a role in open field disrupting the square formation?
There are possible reasons for why the grenades were not used in field:
1. Inconvenience: the effective grenades were too big and too heavy to be easily used.
Rebuttal: Mounted Grenadiers of the Imperial Guard are selected big guys with big horses. Throwing grenades is not too difficult for them. Each grenadier only need to carry one small grenadier.
2. The damage caused by black-powder grenades is limited and not lethal enough.
Rebuttal: the Mounted Grenadiers does not need to kill enemy soldier with grenades. They only need to use a grenade to disrupt enemy square formation. It is unlikely that soldiers are willing to stay in form with a grenade thrown into them. After that, it is easier for cavalry to run them down.