Instead of grease get a longer lasting seal with100 % silicon rtv.
Wait several hours for the battery to depressurize.
Gently wash with a low velocity flow of water to avoid splashing.
Remove cable, wash again, use high speed water to clean out cracks.
Allow to dry completely, use compressed air if available.
Apply a bead of silicone around the terminal. Wearing a rubber glove press the rtv into the plastic around the terminal to fill cracks. Apply another bead around the terminal and reinstall the cable.
Allow to cure overnight before starting engine.