Dead batteries can off-gas hydrogen sulfide, which can be explodey. Also, you don’t know what issues a “dead” battery might be experiencing. There could be a broken post, which could lead to sparks inside of the battery. This is why if there’s going to be a spark, you’d rather it be on the battery that’s less likely to emit hydrogen sulfide, and you want to be away from the battery that’s more likely to go boom or spray.
So, connect the hot dead nipple first, then the hot live nipple. Then the live common (negative, neutral) nipple, and finally, some grounded spot on the dead body. This way, you can avoid sparks near the dead nipples, and possible explosions.
To further the human body metaphor:
One of the reasons you connect the negative jumper cable to bare metal on the car instead of the negative battery post is that terminals corrode and you might not get a good connection with an alligator clamp, but something grounded to the car probably has a decent connection. Similarly, the reason you place AED pads so far from each other on someone is because you’re creating a setup where the heart is somewhere within that path. Could you use less power and cause less damage if the pads were more local to the heart? Yes. But you can’t guarantee accurate placement. So, you pump up the juice, and use any somewhat adjacent known “grounding” point.
They know but only if it’s on the nipples of a person.
Be sure to connect the grounded nipple first.
What??? No!
Dead batteries can off-gas hydrogen sulfide, which can be explodey. Also, you don’t know what issues a “dead” battery might be experiencing. There could be a broken post, which could lead to sparks inside of the battery. This is why if there’s going to be a spark, you’d rather it be on the battery that’s less likely to emit hydrogen sulfide, and you want to be away from the battery that’s more likely to go boom or spray.
So, connect the hot dead nipple first, then the hot live nipple. Then the live common (negative, neutral) nipple, and finally, some grounded spot on the dead body. This way, you can avoid sparks near the dead nipples, and possible explosions.
To further the human body metaphor:
One of the reasons you connect the negative jumper cable to bare metal on the car instead of the negative battery post is that terminals corrode and you might not get a good connection with an alligator clamp, but something grounded to the car probably has a decent connection. Similarly, the reason you place AED pads so far from each other on someone is because you’re creating a setup where the heart is somewhere within that path. Could you use less power and cause less damage if the pads were more local to the heart? Yes. But you can’t guarantee accurate placement. So, you pump up the juice, and use any somewhat adjacent known “grounding” point.