The optimism is almost impressive. Green board, crusty ports, and he thought a fresh battery would fix it. That's like trying to revive a car that's been at the bottom of a lake by just putting air in the tires. Some people see a tech problem and their brain just picks the cheapest possible part to blame.
Man, why do people always think it's just the battery? Honestly, that sounds like a total nightmare to deal with. Three hours of cleaning just to find out it's completely gone is so frustrating. Tbh, some folks just have no idea what actual water damage does. That's a lot of wasted time for you, and a tough lesson for him.