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Comment by LnxPrgr3 | Hacker News Reader

My feelings about that are mixed.

On one hand, I try myself to avoid car battery acid as much as possible. It's legitimately nasty stuff, housed in a device where common use can lead to explosive venting of the battery's contents.

On the other hand, knowing enough about the acid to develop a healthy respect for it is vital to just about everyone in the US. Almost no one I know does jump starts correctly, and a starter battery explosion can permanently blind people.

Everyone ought to learn how to deal with things that are everywhere that can kill or permanently disable someone. Lead-acid batteries are everywhere, including children's toys. Knowing how to deal with them is vital knowledge in this society.

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Is there some particular way I should be jumping a car? I only do it every few years -- and normally end up referring to the manual in the glovebox. Am I missing something?

No, the manual should be correct.

The key is to attach the last negative clamp not to the car's negative battery post, but to a grounded metal object away from the battery. This prevents sparking near the battery that can ignite hydrogen around the battery and cause it to burst.

Yes. You should make the connections in this order: 1) dead battery, positive terminal 2) live battery, positive terminal 3) live battery, negative terminal 4) dead car, unpainted steel on engine block bolt/alternator housing/chassis/etc, as far from battery as practical. This works because the negative terminal of the battery is the chassis ground anyway.

When disconnecting, break the connections in reverse order.

Lead-acid batteries release hydrogen during discharge (and may vent it if the discharge is rapid), or from overcharging (water can electrolyze). So the live battery is likely releasing some, and the dead battery might be if it's actually damaged and not charging properly.

So making the final, sparking connection (or first disconnection) is safest using the negative/ground wire (no potential), on the dead vehicle (avoiding the definitely-discharging live battery), and some distance away from the dead battery (mostly aviding the possibly-outgassing dead battery). This minimizes your chance of the spark igniting a cloud of hydrogen gas and getting a fireball.

And now that you know why the order is what it is, you'll probably be able to remember it :-)

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