Portable jumper cable--negative terminal or car body?


I’ve always connected the black jumper cable to the battery’s negative, black terminal. Lately, instructions are saying to connect the black jumper to the frame (battery trickle charger and portable jumper boxes).




Discharged batteries can emit hydrogen sulfide gas. If a spark occurs within a cloud of this gas, it can explode.

Jump packs usually have an on/off switch which you are supposed to turn on only after you’ve connected both leads, but sometimes people don’t read the manual and turn the thing on before they connect the leads. When they do this, there is a non-zero chance that there could be a spark at the battery terminal which would ignite the gas.


Yeah agree. You want to make the final connection a little bit away from the battery in case there’s a spark.


This isn’t new. I was taught that way over 40 years ago. My 73 Vega owners manual said to connect the negative to body ground…and NOT the ground on the battery.


I guess it’s new to me since I’m reading instructions in later life . Previously, I just followed what I saw others doing.

The explanations make a ton of sense. Particularly, as the instructions say, turn the device on after the cables are connected.




Keep in mind that the car body in many places in not bare metal, and will not provide a reliable ground unless the cable is on bare metal. Unpainted places on the engine block, away from the battery, are good grounds.


The problem is hydrogen gas:


The cables as far as I can tell on any of these small Lithium ion devices are short. Probably the best you could do is connect to a nearby bolt or nut.


In our salt encrusted reg[on, I have found engine grounds to be more reliable than fender grounds.


With the NOCO Genius Boost Plus GB40 1000 Amp jumper arriving today ($99 Amazon). Costco has a Winplus 8000mAh jump starter for $59 on the floor ($89 Amazon). It’s smaller and lighter and has the most important features (auto protect reverse polarity and overcharge).

In light of the answers I’ve gotten here regarding where to clamp the ground, I was surprised to see (on the company’s website) their answer to a QA. The company explicitly says to connect the black clamp to the battery - terminal.

I called the company’s support to make sure and asked. The fellow said absolutely you connect ‘our’ black clamp to the battery - terminal.



That’s because they are SMART jumpers. They will not apply the full capacity to the clamps until they sense the battery voltage for a predetermined time. They know it’s fully connected before they apply the full jump power so it eliminates any chance of a spark.