Jump starting - have I created a problem?

[Gollom]

I jump started my wife's SLK from my S204 yesterday. It has just dawned on me that I used the auxiliary battery to do it - the battery was in the rear on my S211 so I just assumed! Saw something that says it is in the engine bay on S204

All seems OK - hopefully I have not caused any damage?

 

[pmcgsmurf]

I'm confused what battery you used to jump and what battery you jumped to.

 

[markjay]

If both cars drive fine, and all electric consumers work as they should, then you're OK

The potential issue with jumpstarting one car from another is that the front SAM (on either car) could be damaged by a spike.

But you would notice if this happened.

BTW the safe way of jumpstarting a car is from an external fully-charged 12V battery that is not fitted in a vehicle at the time of jumpstarting.

 

[Gollom]

Cheers both

I'm confused what battery you used to jump and what battery you jumped to.

Started the SLK via the engine bay convenience port and earth from the auxillary battery in the load area of the S204

If both cars drive fine, and all electric consumers work as they should, then you're OK
The potential issue with jumpstarting one car from another is that the front SAM (on either car) could be damaged by a spike. But you would notice if this happened.
BTW the safe way of jumpstarting a car is from an external fully-charged 12V battery that is not fitted in a vehicle at the time of jumpstarting.

Yup, aware that external is best but at the time, needs must. Was careful to keep foot well away from accelerator when cars connected and disconnected within a minute of jumping

Thought the battery seemed a little small! LOL It was a post on here about a FIAMM battery that made me put 2 and 2 together!! DOH!

 

[Chrishazle]

I'm confused Steve, my S204 C220 only has 1 battery, a big one in the boot, but my 2008 is pre facelift, not BE and NTG4 so maybe your facelift one is different.

 

[Gollom]

I'm confused Steve, my S204 C220 only has 1 battery, a big one in the boot, but my 2008 is pre facelift, not BE and NTG4 so maybe your facelift one is different.

Hmmmm. I was making an assumption and reflecting something I'd read. Maybe there is another battery in the rear? Sue is out in car at the moment, but will take a look later and feedback. My S204 is facelift with stop/go, but changing battery location is one hell of a change! LOL.

(I thought all C, E and S had 2 batteries)

 

[markjay]

The second smaller auxiliary battery is only present in cars that have the Stop/Start function (generally 2011 and later).

 

[Petrol Pete]

Some have a capacitor instead of a second battery.

 

[markjay]

As above.

On the C-Class, the W204 facelift (frome 2011) had a FIAMM battery in the boot, while the W205 (from 2014) had a capacitor behind the passenger footwell.

 

[pmcgsmurf]

Should be ok if they drive ok without any problems.

I'm of the mind that I simply wont jump a modern car like a W211 (not even that "modern" come to think), just too many bits to go wrong.
I'd disconnect the -ve terminal (on the flat car) and connect the jump leads direct to the flat battery.
Leave for a while to charge the battery (with donor car running) and then reconnect and start.

 

[wongl]

I jump started my wife's SLK from my S204 yesterday. It has just dawned on me that I used the auxiliary battery to do it - the battery was in the rear on my S211 so I just assumed! Saw something that says it is in the engine bay on S204

All seems OK - hopefully I have not caused any damage?

The Aux Battery (if your car has one) should be isolated by relays when the car is off. In other words, putting a battery charger on the main batter will NOT charge the Aux Battery.

Since the Aux Battery is normally isolated this means that when you jump started the SLK, the Aux Battery despite installed in your S204 behaved like a stand-alone battery.

 

[GavinP]

Never had a problem jump starting SWMBO's Golf GT with the S211 or vice versa - just followed the process set out in the owners manual. However, not sure I'd be quite so keen to try it with the S213 but, then again, the owners manual says that you can.

I do remember a Sierra Sapphire GLS losing all central locking when someone used it to jump start a Fiesta.

G

 

[markjay]

...the owners manual says that you can...

I don't think that it does.... I think you will find that the owners manual is showing the car being jump-started from a standalone external battery that is not fitted to another vehicle.

 

[M666LFF]

just jumping on the tail of this .
I have just bought an AA charger maintainer , if I wanted to put this on my w164 would I need to disconnect the battery or would it be OK to leave the car connected the charger instructions seem to say it should be OK

 

[GavinP]

I don't think that it does.... I think you will find that the owners manual is showing the car being jump-started from a standalone external battery that is not fitted to another vehicle.

Taken from the Interactive Owners Manual,

Observe the additional following points during starting assistance:

• Starting assistance may only be provided using batteries with a nominal voltage of 12 V.
• The vehicles must not touch.
• Petrol engine: Only accept starting assistance if the engine and exhaust system are cold.

Inclined to believe their use of the plural makes no sense if donor battery was sitting on the floor!!

G

 

[Chrishazle]

I've been using a battery conditioner on my second car for over 20 years now - first my 968 coupe, then the 968 cab and now the SLK280. It's connected direct to the battery whenever the car is garaged - which is most of the time! Never caused a problem - in fact quite the opposite, means the car always starts first time even when parked up for a long time, and I'm convinced it also seriously enhances battery life as the battery on my 968 coupe was 10 1/2 years old when I sold that car, and was still going strong.

As the S204 lives on the driveway I cannot routinely connect a conditioner to it, instead I have a condition monitor connected to the battery and visible through the tailgate, whenever it turns from green to amber I run an extension lead and connect my SIP smart battery charger direct to the battery. Only been doing this for a few months now, but have not had a problem.

 

[GavinP]

just jumping on the tail of this .
I have just bought an AA charger maintainer , if I wanted to put this on my w164 would I need to disconnect the battery or would it be OK to leave the car connected the charger instructions seem to say it should be OK

Well, I always charged the S211 (for 13 years and only 1 new battery after 10 years) and this new S213 from the connections under bonnet (so battery still connected in under the boot floor).
The S211 had an auxiliary "battery" for SBC etc (no Stop-Start) and that was also changed once.

But as they say "Prior experience is no guarantee of the future"!

G

PS We also have 3 battery banks comprising 7 x 110Ahr units on our narrowboat all AGM. They hold 97% of their charge between visits but are managed with a 50 Amp Intelligent Charger 4 time as year. Rest of the time the twin alternator set up does the rest. I have left it connected and switched on for >3 months without a problem during the really cold winters. First set lasted 17 years.

 

[John]

just jumping on the tail of this .
I have just bought an AA charger maintainer , if I wanted to put this on my w164 would I need to disconnect the battery or would it be OK to leave the car connected the charger instructions seem to say it should be OK

You should be fine.

I've never had an issue charging a modern car with a modern charger with the battery connected.

The caveat is not to try and run anything electric whilst it is being charged (so avoid switching on the ignition).

 

[Bobby Dazzler]

just jumping on the tail of this .
I have just bought an AA charger maintainer , if I wanted to put this on my w164 would I need to disconnect the battery or would it be OK to leave the car connected the charger instructions seem to say it should be OK

It should be fine. I bought a similar device - albeit a CTEK MX5.0 - and hooked it up to the charging post and earth bolt under the bonnet using crocodile clips, and it worked a treat.

 

[jasonh]

The problem with jump starting is "load dump". What happens is you get the car started (so far so good) now the alternator (which can push out 200A or so) maxes out charging the flat battery. Still OK. Now you disconnect the first battery/car and this is where the problem occurs. As you disconnect the battery the load being charged reduces but the alternator is running flat out. The result is a big voltage spike for a moment until everything settles. That spike can destroy car ECU's, pretty much any ECU on the car.

If you jump start from a running second car that car sees a load dump when the jump leads are disconnected so it can be damaged too!

There are various ways to try to minimise the spike - like turning on the rear demist - before disconnecting the jump leads, or letting both vehicles run for a good while before disconnecting the leads. However in a car with a big battery, powerful alternator and lots of ECUs jump starting is a risky business.