ALWAYS WEAR EYE PROTECTION WHEN WORKING WITH CAR BATTERIES, AND NO SMOKING OR OPEN FLAMES!!!!
Use a solution of 3 tablespoons of baking soda in a cup of hot water. Put a KAM unit on the car via the OBDII port, (Keep Alive Memory). This will energize the positive, so be careful with it. Remove the terminals [negative first] and clean them with the solution until it turns back to the correct color. Use rags or paper towels to get all of the solution off the battery and dry the terminals. Use a terminal brush to make everything "bright", and use proper tools to make the connections [positive first] "tight". Coat the terminals with white lithium grease. I have used bearing grease in the past. Some call for other stuff, such as the fluid film. Just be sure to put the terminals on FIRST, then the stuff. Don't forget the KAM unit.
The reader assumes all risks, as I am just someone on the internet giving my opinion.