battery not charging.

stu3.0 · Nov 6, 2016

hello.can anybody help my alternator is not charging my battery but must be working as its running the car. tester on the battery says not charging but a plug in tester inside car says all is working fine.. the battery charges up in the house then goes dead on the car as the alternator dosent seem to be giving any charge to it. thanks

desertstorm · Nov 6, 2016

You won't see any fault codes if the alternator is faulty. If you are measuring the battery voltage when the car is running and only seeing something like 12.5 to 13.3v then the alternator may be putting out some charge but not enough to keep the battery topped up. To charge a battery and maintain it's charge you need at least 13.7v and more like 14V across the battery.
A duff diode in the rectifier pack on the alternator will drop it's output quite considerably as will a short in the stator winding.
You can run a car without any alternator at all. The battery will provide the current to supply all the electrical load however it won't last long depending on how good your battery is and how much electrical load you have. Lights , Heaters, wipers, heated seats, heated windows, mirrors etc really stretch a charging system.
You may get away with just a new regulator on the alternator but probably better to replace it with a remanufactred item as sometimes they are a pain to change.

desertstorm · Nov 6, 2016

@stu3.0 I am not sure why you have posted the same thing across several different forums you just confuse people who are trying to help you as they are unaware of what engine/ car you have. There are some major differences between different models. If you have tried several different batteries then it's not them. It's either the alternator or something that is draining the battery when the car is not running.
What voltage are you seeing on the battery when the engine is idling with no load on. Make sure all the lights are off , the heater fan , heated mirrors , heated screen etc.
Then turn on as many things as you can lights, heated rear screen, fan motor on top speed, heated mirrors what ever you can. And measure the battery voltage. If the alternator is working OK it should hold the battery voltage around 14V .

stu3.0 · Nov 7, 2016

thanks for your help.

stu3.0 · Nov 7, 2016

the car is a A4 b6 3.0 petrol. quattro. ive discovered the ignition barrel is faulty its not turning of when the key is removed.

desertstorm · Nov 7, 2016

Well that would cause a good drain on the battery. SO looks like the alternator is good.

stu3.0 · Nov 7, 2016

i hope so.im having trouble removing the barrel.i know you have to put a small drill bit in the hole next to the key to release it but its not for coming out.i work long hours start 2am till finish so only have limited time to work on my car.thanks for your help.will try to make sure i get on right forum in future.this is by far the best audi site for help.there good cars but can be a bit awkward.

RAF_S7 · Nov 8, 2016

The start of this video may help

DrStrange · Nov 9, 2016

Im no expert but as a result of all this, check the battery with a muti metre to see appropriate charge levels.
Lots of Youtube videos of how to do so.

Im only saying this as after dead alternator (replaced) it has effected my battery so it looks like its on its way out. So this is a common knock on effect.

All the best with it..

desertstorm · Nov 9, 2016

Quite common for a battery to die after having alternator issues, especially if it several years old. When a battery is allowed to discharge to very low levels you get a build up of sulphate on the plates as well as other issues. A failing battery itself can cause the alternator to have to work harder and sometimes it's a bit of a chicken and egg situation.
The Alternator may not have initially failed if the battery condition had been better.
http://www.yuasa.co.uk/info/technical/battery-characteristics-fault-diagnosis/

DrStrange · Nov 23, 2016

Thanks for the info.

I suspect this will eventually happen to mine as the battery is supposedly on its way out.

stu3.0 · Apr 29, 2017

hello the problem continues. ive changed the ignition switch and when i test the wires with ignition of ther now all showing no power so thats not what was draining the battery. some reason alternator is running the far fine but not charging the battery. i know a car runs without an alternator but not all day and night like this still does. i dont have a voltmeter. just a tester that tells me if wires are live or not. in the 90s i had a xr3i that i had to push start everyday then it wud run fine. then a mate of mine said it seems like a wire of and sure enough a little black wire that went from the back of starter motor into the loom had broken of. he said this was the alternator feed . is ther such a wire on these A4s. is this the exciter wire i read about. please any help would be great. im convinced the alternator is good and not at fault here.will purchase a volt meter asap. thanks.

stu3.0 · May 13, 2017

HELP ME PLEASE. fixing to use this thing as fire wood ! ok not really but im stuck.

stu3.0 · May 13, 2017

i got a voltmeter and it shows the alternator working . goes upto 14+volts wen revved etc. 13.2 ish volts at tickover.

vr6gordy · May 14, 2017

Sounds like your battery's not holding charge ... buy a new battery

stu3.0 · May 14, 2017

im on third battery from my other cars that are all fine so its not the battery. i think its the feed from alternator to battery wire broken. the catalyst snapped at downpipe and had to be ripped from under car so we could continue journey was a couple days after this that the car 1st wouldnt start without a jump. was on the passenger side cat .

vr6gordy · May 14, 2017

It's no good just guessing all the time .. if it's out of the range of your capabilities then get someone on it who knows what there doing .. in the long run it will save you money

stu3.0 · May 14, 2017

thanks. not guessing ive established that the alt is working. the batterys im using inc its original are all known to be good and hold charge as normal on my other cars after theyve charged back up. wot i need to know is about this alternator feed wire ! is ther such a wire ? tryed buying haynes manual but the A4 haynes manual dosent cover this model. even says on the back. does not cover 3.0 quattro . and dosent give an alternative. i bought another car for panels (my wings/arches are rusty!) but its not the same spec so the loom is very different although it is a 3.0 V6 quattro it dosent have all the toys/stuff like the driver comp auto adjust lights etc etc. its just the same colour,engine, drive train. car is ok apart from this issue.except the door locks are clickin due to micro switches in doors. i beleive from reading this and other audi sites. thanks again. any advice/ideas is better than none.

stu3.0 · May 14, 2017

its not beyond me . if the alty was bad i could replace it or even repair on bench if needed etc. but its working.this is whats annoying the car runs fine when started even with all lights + heater + rear screen inc amps bass speakers all going etc etc. its just stopped giving charge to the battery. cant afford audi service prices could probaly get another 02 A4 cheaper.

vr6gordy · May 14, 2017

What is the ampage of your alt and what can your battery hold .. might be the alt not making enough power to fill your battery

stu3.0 · Jun 15, 2017

still not charging my battery although i did find a thread that mentioned the mythical "exciter wire" seems it turns the ignition light on and this tells the alternator to start charging if needed.now the light comes on but clearly for some reason the alternator isnt getting the signal or it has decided not to play by the rules of the ECU. im having other issues like a petrol gauge/read out that is not showing true level. and random bulb out warning.says turn signal out then when i turn that signal on at the column the warning goes away and of course all turning signals are working. i dont think this is related as the bulb fuel gauge issue came long before charging issues.

RAF_S7 · Jun 15, 2017

Couple of questions if l may:

Is the battery not being charged, or not holding its charge?

You indicated that you checked the alternator voltage (13.5v at tickover and 14v when revved). Is that measured across the battery terminals or the output of the alternator?

Have you measured the the resistance of the battery -ve (earth) terminal to the engine block, and if so what is the reading?

stu3.0 · Jun 15, 2017

hello. when the battery is charged of the car and used in another car while i try that cars known to be good battery it performs as normal. but then the known to be good battery runs out of charge and i guess the alternator takes over running the car.i know my batterys are all good.they all only dont charge on this car. tested across terminals and also connected to wires on ignition under dash area just because i could. showed increase in volts as expected.low of 12.7V high was 13.7-14V wen revved harder etc. i found a thread about the exciter wire but i didnt save the page. its obviously down to this signal not getting to the alternator.probably something needs re-setting that only the almighty VAG COM engineer can do. simple service code and fault clearing devices dont go deep enough into the ECU.although i cant recall letting the battery go flat.was just flat dead 1 morn and the rest is my nightmare. got a booster/starter thats size of a mobile so at least im not trailing jump leads and xtra battery out of house or constantly with charger under bonnet on drive. so not a total scrapper just yet. but its getting there.

desertstorm · Jun 15, 2017

A battery won't charge with 12.7V across it. To charge a battery you need at least 13.5V and closer to 14V is better. Sounds to me like one of the diodes has failed in the regulator on the alternator. A common problem. Alternators produce AC voltage from 3 coils. This is rectified by a full wave bridge with 6 diodes in to turn it into DC. An alternator should be producing 13.5V at idle even when it has a decent load on it.
https://www.knowyourparts.com/techn...starters-and-alternators-common-misdiagnosis/

RAF_S7 · Jun 16, 2017

The flat dead battery is the symptom of the problem, not the cause, you've proved that by swapping the battery around.

I'm with Dessertstorm on this one. You have alternator issues, likely the diode pack. To be fair, he did say that on post #3 in this thread.

I'm not familiar with the A4B6 to know if the diode pack is a user changeable/repairable, or if you need to swap out the alternator.

stu3.0 · Jun 16, 2017

thanks for all the help on this.although i know all about ac/dc etc i didnt know that 12.7 at tickover indicated the diode trouble. would this explain why the car runs fine but just dosent feed the battery although the volt meter changes when the car is revved and meter is directly onto the battery.its very confusing. ive learnt that thers a wire that lights up the battery light on dash which in turn sends a signal to the alternator to operate.i think this is were the problem is. i think a wire got damaged by the catalyst fallin against the loom at bulkhead.the battery 1st died a couple of days after this. and since my last rant on here ive pulled and pushed on this part of the loom and the revs changed on ther own.thers no throttle cable so hadnt pulled on ewt like that. its all electrical.so im thinking this signal wire has a break in ther somwere. i now need to know which wire this is so i can run a new 1 through the loom. solder new wire on and pull it through. the wires in these is funny stuff ive had to replace drivers door loom due to breakages and discovered 1 in the back door. i assume this is causing a double click to be heard when locking unlocking doors. its on my list to do !! love the car just this issue has killed its appeal.

stu3.0 · Jun 16, 2017

hello. yes the diodes can be replaced on the bench. but by the time you have dismantled the whole front of the car and then if your lucky (it seems) and alternator falls onto your bench ! you probaly CBA (vids on youtube etc) and to just get replacement part easier.

stu3.0 · Jun 18, 2017

ok. now its f××××d. ! LOL.

vwaudimaddkev · Jun 29, 2018

TO CHECK ALTERNATOR START CAR HAVE IT RUNNING THEN TAKE EARTH LEAD OFF IF CAR STILL RUNS YOUR ALTERNATOR IS FINE IF IT CHUCKED IT SHES DUFF

5S-IDUA · Aug 19, 2019

Hi there, know it was a while ago but did you ever get to the bottom of your issue? I had a similar issue on my 2011 Audi S5 3.0T Cabriolet where I would get a 'Weak Battery' message. The Alternator would not charge the battery sometimes, it gradually started getting worse. I brought an OBD scanner and noticed that the starting voltage was 11.8v and would not change even after increasing the idling speed, randomly I'd get 13.2v when it decided to work. Got a new battery, no change. Replaced the Regulator on the existing Alternator - same issue, replaced the Alternator twice - still the same issue. The car sparky found that the single pin cable plugged into the regulator is shorting somewhere as once it was removed the Alternator would charge the battery. It's still unplugged for now so I can drive the car but really want to get to the bottom of this problem. Thinking it could either be the battery module or Gateway Control module but really interested to know what you found to be your problem. Thanks for help.

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