Electricity is a form of energy resulting from the existence of charged particles, electrons and protons. When the charger cable sits unused, the electrons move to the higher parts of the cable, the protons (you guessed it) to the lower areas of the cable. When you start charging it‘s like a garden hose with air in the line.
You should tap the head of the charger on the car to mix up the electrons and protons prior to charging. If you don’t, you‘ll get more electrons than protons and that leads to battery degradation.
For the layperson, think oil and vinegar salad dressing. You gotta shake it up before pouring.
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