I understand that, if charging a car battery without removing it from the car, you should attach the negative crocodile clip not to the negative of the battery but to a metal part of the car; most cars, in fact, have a specific metal thingy to attach clips to for this very reason. There are questions on this, eg here, but I have a few more detailed questions I couldn't find anywhere (I believe the same questions apply to jump-starting, too):
- Why exactly is this? Is it because the clips can always generate a spark, a spark near the battery is dangerous, so you place the negative clip farther from the battery? But couldn't the positive clip generate a spark, too? You should attach positive first, but, also, you should only plug in the mains after you have connected both positive and negative, so does the negative have a higher risk of sparks?
- Is the risk of a spark real only with chargers that use more than 7-8ish ampere? Is it safe to attach a negative clip to the negative battery if the charger is 4A? I'm not saying I will do it, I am just trying to understand the theory behind it.
- How about eyelets and connectors, like the one in the picture below? These can be attached to the negative and positive of the battery, so that, when you want to charge it, you just plug a cable to the connector. But isn't this the same as connecting a negative clip to the negative side of the battery? Or is this safer? If so, why?
- As far as I know the same precaution (not attaching negative to negative) is never mentioned when it comes to motorcycle batteries. Why? Is it because those are smaller (6 to 16 Ah vs 60-90ish Ah for a car) and are typically charged at 0.8A?
- Also, I believe the same precaution does not apply to boats. Is it because the voltage potential through the water would cause electrolytic corrosion? But how is the risk of sparks handled on a boat, then?