Final answer:
The second deadliest battle of the American Revolutionary War that was a failure for the Patriots was the Battle of Bunker Hill.
Step-by-step explanation:
The second deadliest battle of the American Revolutionary War that was a failure for the Patriots was the Battle of Bunker Hill. Although the British technically won the battle by achieving their objective of driving the Americans out of Charlestown, their cost of victory was high, with over 800 wounded soldiers. Furthermore, the battle boosted American confidence while devastating the British forces.