I had to pop to town and pick up my daughters medication and then on my wife’s work; having not used the car for a while its seems the battery was low on charge. There was enough charge for the first start but after a short journey to the pharmacy it wouldn’t re-start.

I was able to get a jump start but I did not know that I shouldn’t connect the leads as per normal, there’s a dedicated earthing point.

The car now starts but has a really rough idle and the accelerator pick-up just pogos, its not consistent. Only just got the car home. its also got an error about internal protection being switched off which I assume is the airbags

Have I screwed the electrics or is it likely to just been down to flat battery……..guess I’ll only know when I get a new battery fitted.

It’s a 2017 Passat

Ah crap!

Worth taking the battery off the car and charging it possibly.

We have a 2017 Audi A6, probably very similar electronics to yours, Christmas eve the battery went flat and it reported all kinds of failures, entertainment system, electric boot, emission control.

It’s worth checking with VW. We called out audi assist who replaced the battery FOC as there was a technical bulletin issued. Start stop batteries are expensive, around £200 and need coding to your car to be fully effective.

its also got an error about internal protection being switched off

Is that relating to the entertainment system perhaps? My Octavia threw a similar message occasionally, it’s an anti-theft measure. If the battery’s been flattened / dead then that might cause it to trip in?

Doesn’t help your immediate issue though. Sounds like the battery’s pooched perhaps.

My guess would be that it’s worth charging and then seeing how the car behaves.

I’ve got a car that is used infrequently and it gives all kinds of spurious messages if you don’t keep it on trickle charge!

Even with stop/start, I would not have thought a new battery should be required at this point in a car’s life – just hope that it’s not ruined the battery going into a state of deep discharge – they don’t seem to like that!

This happens a lot at work, the worst culprits are Mercedes; we’ve had two fail after a flat battery, neither responded to efforts to reset via software, and both had to be trailered to a Mercedes dealer.
Most often it’s just a bunch of error messages that our tech bloke can clear using a BT dongle plugged into the diagnostic port and reset with a handheld device, I think his is a Snap-On using a mobile phone clipped into a larger case.
Clearly there’s no chance of getting help from a dealer, but any of the National mobile breakdown outfits should be able to sort it out in about ten-fifteen minutes.
Like I’ve said, it happens with lots of different modern cars, it’s just down to the amount of computing stuff built into cars these days, I’m afraid.

I did not know that I shouldn’t connect the leads as per normal, there’s a dedicated earthing point.

That shouldn’t make a lot of difference, it’s usually there because the batteries are often stuffed into really awkward places where the clips on the leads often won’t fit, so the manufacturers put a stud bolted direct to the bodywork.
Hybrids can cause some extra issues as well.
Kia Vengas are the worst, the damned things are always going flat, it’s because the boot interior light switch is a bit sensitive, so if the hatch isn’t shut really firmly, the bloody light stays on and the battery goes flat after a couple of days of the car being parked up.
With anywhere up to 3500 cars stored in various locations, dead batteries are an occupational hazard and a royal PITA!

I would have thought an earth is an earth… i.e. the body/chassis/block.
Your issue may be being chased by an undervoltage from the battery. Give it a charge and try again.
I know our fiesta needs to be told when the battery has been replaced – done with a series of actions with the ignition and switches.

(Ign on for 10 secs

press foglamp switch 5 times

press hazard switch 3 times

wait up to 10 seconds while watching battery light

battery light flashes

ign off)

Put battery on charge and try

Modern stuff is so voltage sensitive.

If you’ve just been to the shop and back the battery won’t have recovered. Cars with stop/start need upwards of 5 hours driving at decent speeds to recharge the battery fully.

It might also have an accessory battery to refill as well.

You can get a tool from Amazon for £20 that will tell you the fault codes and reset them, along with the battery voltage over time.

Don’t worry too much about the dedicated earthing point, it’s belts and braces. Some cars shouldn’t be jumped directly to the battery’s positive terminal (Volvos in particular).

My Renault scenic battery went flat so i jumped it off the other car and it took about half an hour of driving before the blowers would work.
It’s a 2010 car, so relatively simple electrics.
I’d say give the battery a proper charge, reset the fault codes then see how it’s running.

Don’t panic yet. Modem cars often do all sorts of stuff when the battery is low. As above, it’ll take a good while if digging to charge it up fully, even if the battery is ok (some AGM batteries don’t like going completely flat though and never really recover)
I’d be sticking the battery on charge for a good while, then trying again.

Thanks all, I’ll be ordering a charger!

The start/stop has been a bit temperamental over the last week which seems to be a symptom of low battery charge.

some cars reset the ecu if you disconnect the battery for a period of time. some cars also need a start up sequence once battery is reconnected. i had a 2004 c max and when it was used to jump start another car the tail gate would lock shut for a couple of weeks. cars do weird shit
think it is possible to turn off the stop start feature in the cars computer while battery is low

Yeah you haven’t ruined anything. Probably a load of errors causing the car to start acting defensively, as above.

Charge it and drive it. The system will ignore some codes if they don’t recur after a period of time or a certain number of starts and it’ll go back to normal.

Get a battery charger – useful in these current times – and make sure it’s a modern smart one that can do start/stop batteries. I have a nice one from Halfords. But do disconnect the negative before charging it if you can.

Spot1978 have you checked to see if the car is under 3 years old. If so call out vw assistance and you maybe able to get the battery replaced foc as part of a technical bulletin. It won’t cost you anything to try if the car is under 3 years old.

That shouldn’t make a lot of difference, it’s usually there because the batteries are often stuffed into really awkward places where the clips on the leads often won’t fit

It’s there to avoid sparks near batteries.

Connecting the final jump lead to the block rather than the -ve terminal has been advice for as long as I can remember driving.

But do disconnect the negative before charging it if you can.

There’s no practical benefit to this.

Some cars shouldn’t be jumped directly to the battery’s positive terminal (Volvos in particular).

I don’t get that – a Volvo is no different to any other vehicle.
A dedicated positive jump start location will simply be connected directly to the battery positive.
As Cougar says…. It’s just for ease of access and to reduce the chance of a spark near the battery which may have emitted flammable gasses.

(I have no idea where the battery in my car is and I’ve had it 6 years 😬)

It’s there to avoid sparks near batteries.

On my car it’s so I don’t have to empty the boot and then remove 2 panels to get to the battery terminals. Sealed batteries fitted to modern cars aren’t likely to be bothered by sparks, and even less so the AGM type commonly used in stop/start systems.

The good news for the OP is that AGM batteries are fairly tolerant of deep discharge, though if the battery was low I’d have expected the car’s ECU to disable the stop/start function.

I don’t get that – a Volvo is no different to any other vehicle.

From Volvo:

When connecting an external starter battery or battery charger, use the car’s charging points in the engine compartment.

The battery terminals on the car’s starter battery in the luggage/cargo area must not be used.

Their emphasis. The battery monitoring system gets confused.

Where does is say anything about the monitoring system?

From the Volvo UK web site
“Warning
The battery can generate oxyhydrogen gas, which is highly explosive. A spark can be formed if a jump lead is connected incorrectly, and this can be enough for the battery to explode.”

Nothing about the monitoring system.

The good news for the OP is that AGM batteries are fairly tolerant of deep discharge, though if the battery was low I’d have expected the car’s ECU to disable the stop/start function.

Not wanting to be a pedant, but this is very much a case of ‘some’ are tolerant to deep cycling. Through stupidity (forgetting to plug the maintenance charger in, mostly) I’ve killed 3 AGM batteries over the years this way.

Where does is[sic] say anything about the monitoring system?

In the service section of the manual:

the energy saving function for infotainment may be temporarily disengaged, and/or the message in the driver display about the starter battery’s state of charge may be temporarily inapplicable, following the connection of an external starter battery or battery charger [directly to the battery terminals]

This specifically cautions about the negative terminal. I was told by a Volvo dealer (that I don’t trust!) that you’d want to avoid connecting directly to the positive terminal as there’s some sort of squib in it to disconnect the battery in a crash. Seems unlikely, personally, but Volvo make the point about six times in the battery description page.

there’s some sort of squib in it to disconnect the battery in a crash. Seems unlikely, personally..

Too right it does!

Through stupidity (forgetting to plug the maintenance charger in, mostly) I’ve killed 3 AGM batteries over the years this way.

Happy to hear of real world experience, while I’ve never ruined an AGM battery myself I’ve only had one in a car for the last 4 years so haven’t had the opportunity to ruin many! As I understand it though they have a greater tolerance to deep discharge than flooded batteries, they’re not immune to it if you’re sufficiently determined.

VW have been having issues with “MOLL” branded batteries, we’ve changed loads under warranty, there was a technical bulletin about it so you may get it replaced by VW assistance if you’re still covered.

Just had a quick look and it is a MOLL. We’ve had it less than two years (second hand) so hopefully it’ll be covered.

Thanks guys