Battery or Alternator ?

lgooch · Dec 18, 2019

Just picked my car up from a bodyshop after somebody kindly ran into my rear end.

Driving home I notice the clock is 2 days out of date and assumed that they must have had the battery disconnected for some reason.

Pulls over to make a phone call. Stop Start kicks in and then a few seconds later I get the RED Battery Logo on the DIS and a message sayign that battery is not being charged.

Started the car up with no issue and drove a little further. Did it again when I was in traffic.

Got my multimeter out when I got home and stragenly I get 18.4 Volts when the car is running and 15.7 Volts when the car is off. I didnt expect to see such high values on 12 v battery but I am in no way electrically minded.

Whats the consensus, battery or Alternator goosed ? Alternator looks like a right pain to replace and battery is the original unit on a 2012 car with £ 82K on it.

Just want an idea before the car lets me down and strands me somewhere and before I spends hundreds on replacing perfectly good parts.

samisnake · Dec 18, 2019

at first read it looks like the alternator is putting out too much power to the battery, but having recently changed my original from new 2011 battery on the car with start/stop, it seems like audi were putting in normal batteries rather than agm or efb. replaced with an agm and no issues since.

BrummieLad · Dec 18, 2019

Your alternator is overcharging the battery by the looks of it. You best sort this asap as this can potentially cause your battery to explode, which is more of a worry than being stranded somewhere. Do you get an intermittent loss of electric power when it occurs I.e power steering, lights, wipers etc....

Sorted the exact same issue on a 8p for someone earlier this year, and that did end up blowing up the battery. The alternator is a bit of a pain on these as the space is tight to get the alternator out, as it gets caught between the engine and rad. Very tight to manovere it there and I ended up taking out the rad to get it out.

Finally make sure you get the right alternator since there two variants, which are are 110a and 140a.

paddy · Dec 18, 2019

You cant get nearly 15v out of a 12v battery so your multimeter is wrong. The battery has six 2v cells.

lgooch · Dec 19, 2019

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lgooch · Dec 19, 2019

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lgooch · Dec 19, 2019

Thanks for the replies guys. The pics above show what I had the multimeter on and they are of the engine running and off. The lower reading obviously with the engine off. I think I had the multimeter set right but if anyone can advise me if I haven’t it would be appreciated. I have stuck it on a normal 9 v domestic battery and get a reading of 12 volts suggesting it is adding 3 v to the reading for some reason.

There is no issue with lights dimming or struggling to start. Car seems quite normal. I am quite worried now about frying my battery due to over charging.

What do you suggest

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lgooch · Dec 19, 2019

paddy said:
You cant get nearly 15v out of a 12v battery so your multimeter is wrong. The battery has six 2v cells.

Exactly what I thought Paddy. It seems my multimeter is adding nearly 3 v to the ready when I put it across a 9v battery. Thsi means I am getting about 12.7 with engine off and just over 15v with the engine running.

aqibi2000 · Dec 19, 2019

Take your multimeter to a 5V source (USB port somewhere) and confirm if it works correctly (4.9-5.1V)

paddy · Dec 19, 2019

Try knocking the meter down to 20v, cant see why that would make a difference even so
If you knock 3v off your readings are pretty much spot on

paddy · Dec 19, 2019

My feeling is if its doing it on stop start its an earth issue, if you could replicate it at a stand still it would be interesting to put a jump lead from the Bat earth to the chassis and see if it cures it. I cant believe a body shop would not disconnect a battery before welding etc .

lgooch · Dec 19, 2019

paddy said:
Try knocking the meter down to 20v, cant see why that would make a difference even so
If you knock 3v off your readings are pretty much spot on

Cheers Paddy

It did it again this morning as soon as I started it up with the engine running.

Just plugged VCDS in and cleared all the codes. (only had one which was a parking sensor - bodyshop)

I have logged the charge and it seems when running the battery is getting 14.8V to it. So maybe now wondering if the bearings or the aux belt on the alternator is on its way out and causing the belt to slip slightly with the bearings grumbling.

Ordered a new multimeter regardless. I dont know whether to just throw a new battery on it and see how it goes (8 years old) or just wait for it to pack up altogether and then renew both the battery and alternator. Really dont fancy freezing my butt off in this weather changing it.

lgooch · Dec 19, 2019

BrummieLad said:
Your alternator is overcharging the battery by the looks of it. You best sort this asap as this can potentially cause your battery to explode, which is more of a worry than being stranded somewhere. Do you get an intermittent loss of electric power when it occurs I.e power steering, lights, wipers etc....

Sorted the exact same issue on a 8p for someone earlier this year, and that did end up blowing up the battery. The alternator is a bit of a pain on these as the space is tight to get the alternator out, as it gets caught between the engine and rad. Very tight to manovere it there and I ended up taking out the rad to get it out.

Finally make sure you get the right alternator since there two variants, which are are 110a and 140a.

No intermittent loss of power at all Brummie Lad. I think I have established my multimeter is pants and ordered a new one. Gives me over readings on everything.

paddy · Dec 19, 2019

I am not an elec guy either but its to much of a coincidence this started with a trip to the body shop....could they have run an elec welder on the car and popped the diodes in the alternator ? Are you getting 14.8 at tick over or at say 3k rpm ?
I used to do electronic work building medical research equip but we never used digital meters as they were nowhere near as accurate as the old needle and dial.

SootySport · Dec 19, 2019

My guess is the battery and alternator voltages are ok if the meter is reading 3v high.
The car needs a long run to get the battery back up to full charge but even then a 7/8 year old battery will be on its last legs, if it’s not dead now the colder weather coming in Jan/Feb will eventually kill it.

lgooch · Dec 19, 2019

Sicne I have cleared the codes the warning message comes on instantly now an stays on. Another plug in with VCDS I think and see if it still shows are charging and a doubel check with my multimeter tomorrow.

vigor · Dec 19, 2019

Hi, I had a 2011 S4 B8 and a couple of years ago I had all sorts of alarms on the dashboard, before everything went off except for the engine. On restarting it all came back to life, but VCDS showed over voltage on every module, around 18.8V. This was fixed by my local dealer by replacing the regulator thar had failed. The various modules shut down to protect themselves.

Hope this helps
Paul

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lgooch · Dec 19, 2019

Just had another play with VCDS before my new multimeter turns up tomorrow. The light stays on all the time now but got the below readings out of VCDS with the car running and then with the engine off with me sat inside it

God I hate cars at the minute !

It seems the alternator is working and the battery holding charge but I think with the age of it and it being sat in a body shop for three weeks then the battery might be toast.

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paddy · Dec 19, 2019

Interesting because i put my Meter on mine today and got 14.2v exactly the same as you.
Call in at a quick fit or the like and get them to do a battery drop test where they just measure the voltage across it with a load.
you could try it yourself by putting your new meter on it and turning on the lights and get someone to push the horn while you watch the meter.
The battery should still read at least 10v + under load with engine off.
As sooty says if it went flat in the body shop which it would if the alarm was on then it needs a full charge to have a fair chance TBH

vigor · Dec 19, 2019

It might look normal now, mine happened on a winter’s snowing evening and there was a lot of electrical items running:
Heater fan with A/C
Wipers
Lights incl front fogs
Heated mirrors
Heated driver seat
B&O hifi

Plus the usual car stuff. Try loading it up to see if you can recreate the fault. On VCDS on the auto scan screen it had reams of modules all with the over voltage fault.

Good luck
Paul

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lgooch · Dec 19, 2019

Those values were with a fair amount of load. AC, Stereo, all lights on etc.

I am gonna get a new battery for it tomorrow and see if it cures it. I really don’t want to do that alternator. Looks like a right pig to get it off and back on.

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paddy · Dec 19, 2019

Its not the alternator, the charge figures are near spot on.

lgooch · Dec 19, 2019

Paddy. Thought as much.

I think three weeks in a cold body shop with an 8 year old battery full of stop starts has managed to send it over the edge.

Trip to Halfords tomorrow then. I will report back for future posters who may want to search the forums.

Thanks all

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lgooch · Dec 21, 2019

So. I drove to Halfords and the light never came on.

Bought a battery

Drove all the way home and in and around town for two days with no warning light appearing.

Says to me the battery lost charge in the body shop

Slammed the new battery on and shat my pants when ABS and steering light wouldn’t go out. Then remembered I just needed to a wheel lock to lock. All now appears just fine

Will have a spin around for a few days and hope it doesn’t reappear.

Thanks for all the help and advice guys. ASN is the best forum around

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