I’ve had this twice now, both batteries were Super Start brand of 3 years or more age. Terminal care had been followed in both instances - a light buffing and then application of waterproof grease.
What initially looked like undercharging from alternator or ground issues grew to be an obvious issue of acid attack to the terminal clamps. Zinc depleted, the pressed brass crumbled.
To limp one car along, I’d slopped on a standard brass replacement clamp - within months it was a weeping mess of zinc sulfate crystals. Have just finished soaking it in a warm bicarbonate solution, it took a change of this to fully neutralise. Erosion of brass is evident in the cleaned, salvaged clamp casting.
