The last big battle was the Siege of Petersburg, where Grant simply waited for the Confederates to run out of manpower. It was followed by a few days of small engagements ending at Appomattox, where the surrender took place.
If you mean 'which battle swung the war?', most people debate between Gettysburg and Vicksburg. (I would cite the latter.)
It was a Union victory.
The Union had victory!both sides claimed victory but it was the union who actually won
The battle was a Union (North) victory.
Victory went to the Union in Tennesse.
The Battle of Anteitim (The Union won this battle) and The Battle of Bull Run (In which the Confederacy had victory).
The Union Army won the Battle of Chattanooga. The victory opened the gate for the invasion of Georgia and the campaign for the conquest of Atlanta.
Since the Confederate General Pemberton surrendered the city to General Grant of the Union Army, I suspect the Union claimed victory.
The Union won but at very heavy costs. Many died on both sides but the south eventually surrendered.
It was the Battle of Prairie Grove that took place in Washington County, Arkansas. It was fought between the Union and the Confederacy, with the Union achieving a strategic victory.
The Battle of Fredericksburg was a lop-side Confederate victory by the Army of Northern Virginia under command of general Robert E. Lee.
The Battle Of Gettysburg resulted in a Union (US) victory over the Rebels (CSA)
When it was won by the Union, Lincoln used the victory to promote his idea of stopping slavery.