My husband said it is caused by the vapor from the battery acid.
It is the vapor of the battery acid leaking out of the battery, so the above answer is correct.
The car battery is NOT dead, it is suffering from the effects of corrosion!
A very thin smear of Copper Grease over the Battery terminal / Cable end will help pevent corrosion.
Don't fix it...replace it.
Yes. The battery post only has to have very little corrosion to make you car not start.
Clean it with a mixture of baking soda and water.
It will help, but a much better solution is to remove the battery cables, clean the connections and then use baking soda to neutralize the corrosion.
It was difficult taking the leads off the very old car battery; the buildup of corrosion was extreme.
If there is corrosion on the terminals then you will have a bad connection that will not transfer power from the battery to the starter. It is just like disconnecting the cable. Electrical current cannot flow properly through the corrosion,
no it doesn't Corrosion on the top of a car battery can allow electrical flow from one post to the other which will drain the battery.
Best is a wire brush and baking soda. You can use grease to coat the terminals to slow down the corrosion.
corrosion of copper, from battery acid vapors, most likely.
A mixture of baking soda and water. Rinse with clean water.