All the replies about cleaning are spot on,after they are cleaned up I would use
This to coat the battery ends and put
These under the cable ends,coat all with the battery protector.
In my Former Rental that was how it was done,I talked to the garage foreman about this when I saw it, He said that he had used this method for over 16 years that he worked there and had no corrosion problems with his fleet.If it is good enough for fleet and commercial use I think it is good for me.
When I replaced my batteries 3 years ago this is what I used,everything is corrosion free.