Battery jump start - negative terminal or grounding point?

[Ice Rich]

Hello,

Just had to jump start another vehicle and the battery position placement on their car was so poorly designed it was impossible to put lead on negative terminal so I used a grounding point and vehicle started fine (positive terminal had clear access).
This got me thinking (and would explain why negative terminal was hidden) - is it always best to just use the grounding point rather then negative terminal?

 

[Rroff]

It is generally safer to ground one end of the negative cable.

 

[joey1211]

In my father's Citroen Picasso you can't get the jumper cable anywhere near the negative terminal. There's a dedicated grounding point to use instead.

Quoted from the AA website

Take the black jump lead and attach it to the negative (-) terminal on the working battery.
Then attach the other end to an earthing point (unpainted metal on the engine block or chassis) well away from the flat battery and fuel system

Oh, and this from another website...

A damaged battery has the potential to start a fire when placing the jumper cables on. Car batteries contain sulfuric acid that can become vapors, leaking out of vents. These vapors can be highly flammable. Jumper cables are known to cause sparks and can ignite these vapors, causing fires or even possibly an explosion

 

[Ice Rich]

Got it, thanks both

 

[gc123]

same for c-max/galaxy new shape and probably most newer cars etc batteries are buried under front scuttles

 

[Ice Rich]

Yep , it was a c-max

 

[iamdjdz]

Had more success in the past with grounding points than negative terminal, not sure of the science but last car I tried to start (Citroën C3 off a BMW 320d) wouldn't start on the battery but started first time on grounding point.

 

[MrRockliffe]

Also - don’t use the connected battery/car to start the engine of the car with the dead battery.

You should start the engine of the working car so that it charges the dead battery enough to start it You can damage the working car if you don’t do this

 

[bobuk]

Better off not jump starting modern cars can cause a lot of damage to moders engine management systems

 

[Rroff]

Better off not jump starting modern cars can cause a lot of damage to moders engine management systems

Should be OK if doing it just to get enough charge into the other battery to get it started that way - don't recommend trying to jump start with the donor vehicle still connected up - seen it cause problems with the ECU/immobiliser before.

 

[Chris Wilson]

If the current sense module is in the negative battery lead, (or both as they are on some vehicles), grounding at a point after the battery terminal could "confuse" elements of a CAN-BUS system and cause "issues". It's not something I have personally experienced but a couple of colleagues claim they have seen this.

Modern ECUs and CAN-BUS modules are very well protected against voltage and current spikes, and against reverse polarity, but it pays to not be Cavalier when connecting a jump start battery or vehicle.

Some commercial size booster / chargers are horrendously dirty on boost start, even when connected the right way around. I am very wary of any I haven't had a 'scope on, to look at the output waveform.