The German Mercenary soldiers were trained extensively. The army of Frederick the Great of Prussia was the basis of their training, and many armies afterwards have been fashioned after it. These soldiers brought their own guns and other equipment to the battles. Yet they had supply problems, also. Their supplies came from Germany and had to go through a supply depot, possibly in England, and then come to America. When the soldiers first came, they had been told that they would be issued shoes and uniforms. What they were issued were ladies slippers and cheaply made coats. After a year of being made fun of, the German soldiers eventually got their real supplies.
The German soldiers, even though they had no real belief in the cause, were forced to swear allegiance to the King of England before they could come to America to fight. If soldiers were to leave, they would be considered deserters. Quite a few did desert, and the numbers of German-Americans in Pennsylvania shows this. General Custer's descendent actually fought in the Battle of Saratoga.
Fifty percent of the soldiers at Saratoga were German. This is a much larger number than many people believe. They simply aren't aware of the different armies that actually made up the British army.