During the Napoleonic era, are there any accounts of grenadiers dropping their grenades before throwing them or their Grenades colliding with each other when thrown? How would this sort of error be avoided when fighting in formation?
The "grenading" function of the grenadier was already obsolete before the Napoleonic wars; to find a grenadier actually throwing a grenade, look to the 17th and early 18th centuries. There are few accounts if it being useful even at the time of its invention.
By the time of the Napoleonic Wars, Grenadiers are elite troops with flash uniforms and social prestige, rather than actually using grenades, Charles James in his "Military Dictionary" compiled during the Napoleonic Wars[1810] says that "grenades have unaccountably sunk into disuse". Think of paratroopers in many contemporary armies, who haven't done a combat jump in decades. The Grenadiers' distinction tended to be that they were tall and/or veterans; in armies often drawn from men who were malnourished and consequently small by modern standards, a group of men six feet or nearly was impressive when the average soldier's height was more like 5'5".
There's an excellent piece in Scientific American in 1906, by a British officer, by a LT.-COL. C. FIELD, of the Royal Marine Light Infantry, entitled "Grenades and Grenadiers"; he's writing about the novel use of grenades in the Russo-Japanese War, and the fact that they hadn't really been used for a very long time.
By the time the fur cap came into wear the grenadiers had to a very large extent given up the use of the hand grenade, but the grenadier companies were still composed of the biggest and finest men in the different regiments. Toward the end of the eighteenth century it became the custom to form grenadier and light infantry battalions provisionally from these companies of the different regiments employed together on an expedition or campaign.
Looking through late 18th century accounts of battles in which Grenadiers took part, I can't find anyone mentioning using a grenade. So, for example in the American Revolutionary battle of Germantown, there are both Hessian and British Grenadier regiments present; no mention of grenades in use, even in the close quarters where one might use them-- instead they're fixing bayonets; can't really do that and prepare a grenade at the same time.
Similarly at the Battle of Monmouth we hear of
two companies of British grenadiers of the first battalion that made the charge with bayonets through the wood at Freehold
A cursory search of Napoleonic battle literature with the term "grenade" finds only decorative uses, viz
During his Egyptian campaign Napoleon systematized the granting of awards for the march on Syria. Drummers were to receive silver drumsticks; trumpeters, silver trumpets; artillerymen, silver grenades to attach to their crossbelts;
Sources:
The Battle of Germantown Described by a Hessian Officer
Notes on the Battle of Monmouth
Toward an Army of Honor: The Moral Evolution of the French Army, 1789-1815
European Heights in the Early 18th Century
A new and enlarged military dictionary, 3rd Edition, 1810