Only had the car seven years so I think I can be forgiven for not having noticed the little black plastic cap screwed on to a short threaded stub adjacent to the battery.

 

I only realised it was there today whilst Googling info about jump starting and charging batteries.

 

I now know it's an earthing point to clamp the negative lead on to but didn't see a reference to it in the "battery charging" section of the handbook.  In fact the book tell me to connect the negative lead to "a solid metal part which connected firmly to the engine block or the engine block itself"

 

However I'm a bit confused as, presumably, part of the reason for connecting the negative lead to the aforementioned purpose made stud was to save making a connection on the battery's negative terminal with the resultant chance of creating a spark which might ignite the combustible gases etc. etc. - but if that were to be the case then why did they site the stud so close to the battery?

 

The book says I can use the battery terminals when connecting a battery charger but I wonder if I could/should use the stub for the charger's negative lead ... and why might I want to do that anyway?

 

Answers on a postcard please.

Nothing to do with sparks or gases, but to do with electrical spikes that can happen when you either jump start or use some poor quality chargers. It is especially important when the car is equipped with the different batteries needed for the stop/start system.

If your book says you can go straight to the battery then do so, but you could also use the stud. Both will do the job.

From the manual.
""The jump-start cable must be connected to the engine earthing point only on vehicles with the START-STOP system""

2 hours ago, Urrell said:

From the manual.
""The jump-start cable must be connected to the engine earthing point only on vehicles with the START-STOP system""

 

My book doesn't mention "stop/start".

Nor does it mention the stud.

There are countless references online, some by ostensibly authoritative sources, that refer to avoiding the negative terminal to avoid the risk of igniting the gases ... they also say keep clear of fuel lines for similar reasons. So presumably they DO consider there to be a risk of sparks and gases.

I quoted, above, what it does say about using the engine block etc.

 

I'm only quoting what I see written.

 

I'm not sure I'm any wiser.

Can you post a picture of this stud, without the cap on?

Almost certainly - but these hi - tech assignments take me a little longer than most.  Give me a hour or three and I'll be back......

No rush.

 

I've done the deed. I'll have a go at posting it  .....  this might take a while :-)

Above is the blighter. The plastic cap that screws on to it is just to the left (above the "V" of Varta.

 

You can see it's attached to a stout (negative??)  cable.

Edited 6 November, 20187 yr by oldstan

Does that stout cable go to the battery's negative post, or to the engine?

I'll have a look.

Straight to the negative post.

OK, so it's the main battery to chassis ground connection. Presumably held on by more than just the plastic cap!

 

I reckon the sparking / igniting gases possibility is still favourite as a reason to connect charger or jumpleads to that rather than the battery post itself. (Unless there's stop/start systems and battery management modules involved).

It looks like the battery posts are on the other side of the battery from what you've pictured, and they're probably the most likely places for any gases to emerge as the posts already cross from inside to outside the casing. Dilution with distance would be fairly fast I should think.

 

It would shorten the path slightly to the starter motor for jump starting if you use that (eliminating the resistance of that stout lead and it's terminations), compared to going straight onto the battery post. Very marginal improvement though, unless that lead had serious issues.

 

All received and understood. Ta muchly. Appreciated.

 

(and, yes, the plastic cap is only that - the stud is firmly affixed to the bodywork).

 

The battery is brand new so I think we'll be OK for a bit but it's nice to know a little bit about these things.  I have jump leads in the shed but was always wary of ever using them ( on my own car or anyone else's) in case we upset the electronics.

 

I did bring this up in 2011.  I'll see if I can find the link.

 

 

hold on ....

 

here it is ...

 

17 hours ago, oldstan said:

My book doesn't mention "stop/start".

 

Doesn't seem to be in the manual until the November 2013 edition.  Must say I thought the Greenline models had stop-start earlier than that but very prepared to be wrong...(more than used to it!)

Few fires and explosions, and they saw the need for the extra terminal and change in procedures?