But don't know why the chalky stuff builds up on the strap
What we do to prevent this is disconnect everything, clean everythiing with baking soda and water, this removes all old corrosion build up. We then reconnect everything and coat all metal with vaseline.
There are many commercial products out there for cleaning and protective sprays but we find this has worked the best for us. We make sure to only fill our battery chambers to not more than 1/4 inch above the plates.
Many times this chalky stuff is a result of the batteries being over charged.