The green stuff on your vehicles battery terminals is just corrosion buildup that occurs either due to overcharging or undercharging of the vehicles battery.
It's also known as sulfate and mostly occurs due to undercharged batteries.
If the corrosion is occurring on the negative terminal of the vehicles battery, your system is probably undercharging and if the corrosion occurs on the positive terminal then it's likely overcharging.
You can remove corrosion safely from vehicle battery terminals by mixing some baking soda and water together and pouring on the vehicles battery terminals and let it sit for 20 to 30 minutes to remove the corrosion.
Then just use a garden hose and rinse the battery terminals off with the water.
It's best to remove the battery connections and clean those up really good because the battery could be undercharging due to bad connections from the alternator to the battery.