Corroded batteries are not dangerous but you should still avoid touching the battery corrosion with your bare hands.
If you need to clean battery corrosion you should wear gloves and use some baking soda and warm water to clean the battery corrosion off.
When your cars battery has corrosion you can mix some baking soda and warm water together and then pour the baking soda and water mixture onto the corrosion on the car battery.
Allow it to work for around 5 to 10 minutes.
Then use a wire brush to help brush off the battery corrosion and then use a hose to wash the corrosion away.
Battery corrosion can make a battery seem like it's dead because it can prevent charging of the battery through the alternator and also make a bad contact where the starter may or may not engage.