What battle was the turning point of the American Revolution?
In my opinion it was the Battle of Trenton December 26, 1776.
Trenton was the American's first victory since the battles of Lexington and Concord more than a year and a half before.
Once Washington had taken Trenton, he proceeded to push the British back out of New Jersey and into New York.
That set the stage for his attack in late 1777 on Philadelphia to route the British from there. Unfortunately he lost the first two forays at Brandywine and Germantown. But such is the war of attrition when one side can call upon reserves and the other side has none, the latter being the British. Gen. Howe resigned as British commander in chief and was replace by Gen. George Clinton. At the same time the French came to the defense of the Americans.
The reason these two need to be put together it that had the Americans lost the Battle of Trenton, it may well have been the death knell for the Continental Army. Instead, it reinvigorated it.