Car jump starter box connections?

just connect it to any metal part it does the same thing as grounding it to the battery since the hole body is grounded to the battery neg.

There is a good reason to use the earth to ground method :-

It makes no difference if you connect to + battery terminal and to the metal chassis or the - terminal on the battery. The reason is one of safety.

When a Battery is charging or has had a charge put to it gas is produced, this Gas is explosive. Once the Car has started or not as the case may be. You would remove the( -) jump lead first.

As it is away from the battery if there is a small spark it is less likely to ignite any gas from the battery and when a battery explodes it does go with a BIG BANG. ( It is rare but it can happen).

Like many other things common sense must prevail. There is nothing to fear just take care.

any time you use jumper cables or rechargeable started battery pack you, it is much safer to hook to positive side of the battery and the negative cable to a good grounded part of your engine. this is done to keep a battery from exploding, when you use both terminals on the battery, what happens sometimes gases built inside the battery, when hooking directly to the battery, and battery explodes and the acid could burn someone

For years jumping a battery was + to + and - to - on the battery. Now the proper was is

+ to + and - to cheesy ground or some place on the motor, not to the battery. It will work ether way and no you have not been doing it wrong.