At the scale of a laptop battery, just putting it somewhere without flammables around is sufficient. A bucket of water will absolutely stop anything from happening due to the strong cooling effect. This is not a car battery where water can not actually reach the individual cells. However, I also understand your concerns.
But if I should think of a way for a random person to deal with a dangerous battery in an enclosed space, a bucket of water would be very high on the list. Even if it is already burning.