Can a bad alternator drain the battery when the car is shut off?

Igotadose

Trying to diagnose why my 2011 Auris's battery goes dead overnight when the car is turned off. Everything electric-related is turned off, lights, radio, doors shut, dome light, etc. If the battery is attached, it's dead in the a.m. It's a fairly new battery (September.)

Dealer's mechanic claiming I need a new alternator. I can't see why the battery, when charged after hours of driving, would drain and I expect if I replace the alternator, nothing will improve.

Dealer had the car overnight, and it was not dead the following a.m., but the battery was well charged as its a 1.5 hour drive to the dealer.

My gut tells me it must be something else, but no way to diagnose it. Suggestions as to how to direct the dealer's investigation?

FWIW, since the car sat at the dealer overnight and wasn't dead, it obviously can't be the alternator since it's still the original alternator.

XsApollo

why do you think the battery is fully charged after driving?

Your battery won’t be charged after driving if the alternator is faulty,

that’s probably what the dealer is trying to tell you, that the alternator is not charging the battery.

take the car to an auto electrician, surely they can check if the alternator is working correctly or not, or probably the mechanic has already checked what the alternator is doing.

Flinty997

Might not be charged. Might be getting an intermittent charge when driving which is just enough to start it once or twice but not after overnight. At least sometimes.

I've had this with a failing alternator. But also had it with a cracked battery connector clamp. In both case an intermittent fault was hard to diagnose as often was all tested fine on a static car.

But you'll know if they test the battery in the morning. If the dealers not giving you enough information get a 2nd opinion by getting it checked with an auto electrician. Dealers are very quick to throw parts at a problem at your expense.

vandriver

I've just had an alternator replaced on my Caddy taxi for exactly the symptoms you describe.It *might* start in the morning if I'd driven it the night before,but Saturday night to Monday morning,no chance.

New alternator,new battery.....new car!

mickdw

https://www.boards.ie/discussion/2058323243/can-a-bad-alternator-drain-the-battery-when-the-car-is-shut-off

Even if charging perfectly when driving, a fault in the alternator can absolutely discharge the battery when turned off.

A faulty rectifier in the alternator can cause non start after a very short period sitting.

Leaving ignition switched on will drain battery quickly. Alternator fault can produce the same result.

Igotadose

Thanks to everyone for their replies. Much appreciated. I will see if I can find an auto electrician for testing.

mickdw

https://www.boards.ie/discussion/comment/121387584#Comment_121387584

You appear to refuse to acknowledge that it can be the alternator at fault as diagnosed by main dealer.

Buffman

https://www.boards.ie/discussion/2058323243/can-a-bad-alternator-drain-the-battery-when-the-car-is-shut-off

It's the alternator that charges the battery, not the engine. If your battery is new then it 100% sounds like an alternator issue. If I was you I'd hope it's the alternator as it's an 'easy' fix, otherwise it means you've a parasitic drain somewhere and they can be a nightmare to sort out.

I don't see why you think 'it obviously can't be the alternator since it's still the original alternator'. That makes it far more likely that your 12 year old alternator has an issue. Brushes and other parts do wear with use.

Also, going to a dealer with a 12 year old car isn't the most economical way to get it sorted, a local independent will sort you out for less. A rebuilt alternator with exchange of your old one would be cheaper than new also.

https://www.boards.ie/discussion/comment/121387584#Comment_121387584

It's very simple to test yourself with a Voltmeter.

https://www.youtube.com/watch?v=LGB6ZEjGm7Q

Water John

Doesn't diagnose your problem, but a lot of people with older tractors and plant fit dead switches which are turned off each night, to prevent any stray drain, which can often crop up in older machinery.

Flinty997

https://www.boards.ie/discussion/comment/121387662#Comment_121387662

People not trusting dealers is a rod they've made for their own back.

Though equally bringing an old car to main dealer is an odd thing to be doing.

I've just been shopping for a car and the lack of basic knowledge about their own cars by the sales staff was truly impressive.

RiderOnTheStorm

Im surprised no one has mentioned that the battery itself might be at fault. If the alternator is ok, and the battery is bad, then the charge going in during a run will not be stored properly (damaged cells?). But back to prev posters .... you need to get it (battery & alt) checked. On a 2011 car, a new battery is more likely than a new alternator imho.

Igotadose

https://www.boards.ie/discussion/comment/121391264#Comment_121391264

The battery is new (September.)

BorneTobyWilde

They'd be a light on the dash if the alternator was not charging Shirley ? I'd say it's a battery you need, if there is no light. Normal to replace a battery, try that first, if the problem is still there then take it from there, but battery is first step, anyone selling a battery will fit for free.

Flinty997

No light when I had alternator problems. They were older cars, so perhaps didn't have the checks modern cars do..

JIdontknow

What's the voltage across battery terminals when the car is just switched off after running, and what's it in the morning before you try start it (This will tell if there is a leak or the battery is potentially faulty) ? And also as you start it what does the battery voltage drop to? I had a problem before where sometimes my car would start and other times nothing, was random too like it might start after 12 hours but mightn't start after a few or vica versa. Turned out to be a cell in the battery (The battery was 8-10 years old in my case) when I checked the voltages.

mickdw

It's a problem when the car is switched off.

Alternator can be charging fine but have an internal fault that can drain the battery when you turn off the car.

It could be other things of course but it's a reasonably common fault.

Some of the opels were known for this type of fault.

Alun

Don't assume just because it's a new battery that it's 100% OK. We had a new battery fitted in my wife's car at a main dealer a few years ago, and it was completely dead within a week. They replaced it with a new one, and the problem was solved.

Igotadose

https://www.boards.ie/discussion/comment/121391899#Comment_121391899

Car got battery replaced in September and .no problems until 10 days ago.

Buffman

Lads, don't forget a mechanic has actually inspected this car and said it's the alternator and there is absolutely no reason given to think it isn't.

https://www.boards.ie/discussion/comment/121392296#Comment_121392296

Apart from your 'gut feeling', is there any particular reason you think the mechanic is lying to you? An alternator has a finite lifespan before a rebuild is required and you've done well to get 12 years out of the original. An alternator might not go bang and die enough to trigger the dash warning light, they can die slowly over time and eventually reduce their supply voltage to a level that can no longer sustain all the cars requirements.

The mechanics OBD scan would have told him exactly what the issues are.

Igotadose

https://www.boards.ie/discussion/comment/121392723#Comment_121392723

Picked up the car today, the dealer's mechanic said he couldn't say that the alternator was causing the draining problem. They'd not done anything other than measure the battery voltage. I took the car to another mechanic who had worked on the car previously but wasn't available when I was trying to get the car looked at last week. He'll fit it in, knows exactly what to do and test for.

My 'gut feeling' was because I charged the car for a few hours on a trickle charger when it was dead, measured the charge (9.6V) and let the car sit overnight. Next a.m. the charge was, I think, around 7V, at which point I scrambled to find someone to look at it, came up with the dealer, got the car jumped and drove it in. It never failed to start for the dealer even sitting on his lot for the weekend, nor did they provide any information beyond that the alternator wasn't charging the battery 'fully,' that the car needs new spark plugs (something I hadn't asked them to look at but they said its because 'the alternator and spark plugs are part of one system'), and oh it was hard starting do you have compression problems, where the car has started reliably for the 8 years I've owned it, except recently when the battery died.

Based on the feedback here, and what I could dig up, the alternator could indeed be the problem, but I certainly wasn't comfortable leaving it with the dealer's mechanic, who was very unhappy that I was coming simply to pick up the car and not signing up for his alternator job (at 750+ euros)

kippy

Jesus, this is usually a fairly open and shut case. Straightforward job for any mechanic to troubleshoot this with a multimeter one would think.

The Continental Op

A car battery that has been allowed to discharge to 7V is about as much use as a chocolate teapot. It will work for a bit but will never be any good ever again.

Igotadose

https://www.boards.ie/discussion/comment/121392991#Comment_121392991

I expect the new mechanic will test it and, if necessary, we'll replace it. I agree, if a new one is needed, so be it. What was interesting in both cases is that the car was turned off. Oh, when the battery is charged but disconnected from the car, it holds the full charge no problem.

The Continental Op

At the very least discharging to that level (7V) will reduce the life of the battery.

Igotadose

https://www.boards.ie/discussion/comment/121393057#Comment_121393057

Thanks for this information. This thread's been great for finding out what the car's problem might be, thanks to all the contributors. PM me if you want to know the problem dealer 😉

JP 1800

It is very straight forward to check a vehicles electrical charging system, not much has changed since the late 60s when alternators were replacing dynamos. The checking of a vehicles charging system is a basic component in the vehicle maintenance training module. To check the battery: with all electical systems off, check voltage, a voltage of 12.4-12.6V should be present, 12.6V indicates fully charged battery, 12.4 is 75% charge and 12.2 is 50% charged. A voltage of 12V indicated battery is very low on charge. If low; charge battery with charger and check again. To check health and capacity of the battery, remove fuel pump fuse and check battery whilst cranking engine for 5 - 10 seconds. Voltage should not drop below 9.6V, if it does battery is deffective or soon to be deffective. To check alternator, start and run the engine, check voltage on battery which should show 14.2 -14.4V, this would indicate alternator is charging battery, next turn on headflights, heater, blower etc to load the system, the voltage should drop and then rebound to 14.4V. If not the altermator is showing signs of braking down and unable to maintain a charge. Obviuosly check connections and belts for tension before replacing the alternator. This is very basic stuff that any competent technician should know. To check for paracitic draw, one has to systematically check for a current draw on each system and eliminate by pulling fuses. When a current draw drops with the removal of a fuse, that indicated the circuit at fault. Again basic stuff.

JP 1800

Also to add to other posters comments if a battery dropped to 7V the damage has been done to the battery. It may be savable by de-sulphanation cycle on a charger but they are never at full capacity afterwards and it is best to replace as it will let you down on a cold morning.

PukkaStukka

I had the alternator in my sister's Fiesta drain the battery overnight. After eliminating everything else, I disconnected the thick red cable from the alternator to isolate it. The next day, the car started fine and battery volts were perfect. Once replaced, the issue never reoccurred

mk7r

https://www.boards.ie/discussion/comment/121393155#Comment_121393155

In the last ten - fifteen years car have tended more towards smart charge system so the alternator can produce between 12v and 17v depending on load, state of charge of battery etc so it's a little more complicated than that

jmreire

https://www.boards.ie/discussion/comment/121392296#Comment_121392296

Obviously, its leaking current even when everything is switched off, so that should show on a meter. One thing you could do is after a long drive, and with the battery fully charged, disconnect the positive cable from the battery at night. Reconnect the next morning and see how it behaves. If it bursts into life, that rules out the battery. If it doesn't, then it's the battery.

Buffman

https://www.boards.ie/discussion/comment/121392977#Comment_121392977

Ye, as I said above, a dealer would not be the most economical way to get it sorted and the €750 quote shows that.

As mentioned by JP, a good battery should be sitting around 12.5V so when you measured it at 9.6V it was still way down. I'd guess the dealers charged it fully and that may be why it didn't die while with them.

Hopefully you get sorted with your usual guy.

Hellrazer

Your new battery is fecked if its dropping to 7v over night.

For a car battery to loose that overnight you`d have to have something quite power hungry causing the drain and an alternator wouldnt be where Id start - I dont remember ever seeing a faulty alternator drain a battery.

My opinion - theres a dead cell or cells in the new battery - not that unusual especially if the battery was sitting on a cold concrete floor in the factors. . You say it was ok up until 10 days ago?

Probably the start of the colder nights and thats whats killing it.

Id get a multimeter and see what its charging at - should be around 13.5 - 14 volts.

If its charging at that then the alternator is good.

Then check the battery for voltage - usually around 12.5 is fine. Leave it overnight and check in the morning - it should really only lose around 1 volt. Any more than that Id charge it up again and the next night disconnect the red battery cable and check it the next morning. If it loses more than 1 volt again its 100% the battery.

Igotadose

So, after 2 weeks of investigation, all that was found, was a fault logged by the computer about the control box next to the battery. The mechanic wasn't sure it would fix the problem and advised us to take it home and wait and see. He had tested the battery each morning and looked for parasitic devices and tested the alternator, nothing. I'm confident he tested everything he's quite savvy about car electrical systems. This isn't the dealership who had no clue and lots of attitude.

I've since acquired a 'jump charger' box that should bail me out should the battery go dead again. Nifty thing, charges on USB and includes a torch.

In the last 10 days or so, the car has started fine every morning. We picked up the car on Tuesday, it was fine.

Wednesday morning, the key fobs again stopped working. This is what happened when this saga began, the key fobs stopped working a few days before the battery died.

Should we replace the control box? Could that be causing the problem? The mechanic said we didn't need a new battery, so at this point, I think I'm going to let it go and see what happens.

mickdw

So your main dealer diagnosed alternator.

Your expert auto electrician diagnosed feck all and now you are no further along other than deciding to carry a jumpstarter.

Main dealer as stupid as they can be would clearly have read the same fault your guy did. They may however have seen the issue 100 times before and know that fault at control box is result of alternator issue or may have factory technical data directing them that way.

I have seen alternator causing this kind of issue.

FREDNISMO

Had a similar problem on my car, turned out to be a short on starter motor that was draining battery overnight, new starter motor no problems since, took a while to find problem.

Igotadose

Well, it's died again. Seriously thinking of scrapping it at this point; an alternator, a new battery and a control box is a bit much to spend right now. Will try jump starting tomorrow.

Sure does seem like the cold weather here is part of the problem; when the car was at the mechanic(s) it never failed to start, but it was stored indoors or was out in warmer weather than we've had here the last few days.

mk7r

https://www.boards.ie/discussion/comment/121453464#Comment_121453464

This really points towards the battery itself, not a drain on the battery.

Igotadose

https://www.boards.ie/discussion/comment/121453741#Comment_121453741

Hmm. Battery just measured 7.6V. I plan to measure & boost it tomorrow and drive it around - don't feel it would be wise to drive it around tonight with weird problems occurring.

mickdw

https://www.boards.ie/discussion/comment/121453741#Comment_121453741

It sure does.

The Continental Op

https://www.boards.ie/discussion/comment/121453752#Comment_121453752

It doesn't matter what other problem you have that battery being drained to 7.6V yet again will seriously degrade the battery therefore you need a new battery even if you find and fix another issue.

mikewest

Have you brought the car to wherever you bought the battery and told them the battery is not holding charge. If you got a new one this year then that battery is under warranty. Get it replaced, may need to get firm with them. If the new battery is still giving trouble then it's either the alternator or a phantom drain.

Igotadose

https://www.boards.ie/discussion/comment/121453776#Comment_121453776

That's likely to be the next step.

I remember in the old days you could test batteries with a gizmo that had little colored balls in it, I think you went from cell to cell and looked at how many floated. I expect those days are over, is there any other way to test a battery?

BTW, we didn't care about safety as much back then (I'm thinking mid 1970's).

mickdw

https://www.boards.ie/discussion/comment/121453776#Comment_121453776

And would you go back and apologise and pay for the replacement battery if you then found it wasn't the battery.

mikewest

Yes but most likely they would test the battery and find out if that one was faulty first, easy way to get a simple diagnosis of one possible fault.

mikewest

If they sell a decent quantity of batteries they will have some form of tester or know there is a certain failure rate of the battery they supplied you with.

mickdw

https://www.boards.ie/discussion/comment/121453863#Comment_121453863

Ya but that's a different story to - go back, get firm and get it replaced.

If it does happen to be battery in this case, testing will likely tell us nothing as its operating fine for periods then no start.

I've seen battery cracked around the terminal behaving in this way and causing awful hassle.

Andrewf20

Had a similar issue on my E36 recently. When the engine got turned off you could see the battery voltage drop approx 1 volt every 5 mins. I disconnected the positive battery cable and found 3 ohms resistance between it and the chassis. I pulled each fuse one at a time and rechecked the cable to chassis voltage each time until I found the fuse that when pulled out, gave open circuit. The fuse was for the interior lights and cigarette socket. It was a faulty USB charger plugged into the cigarette socket that was draining the battery but strangely not blowing a fuse.

mk7r

https://www.boards.ie/discussion/comment/121454202#Comment_121454202

It wouldn't blow a fuse unless the current draw exceeded the value of the fuse (20A). It could happily sit there and draw 15A all night long being faulty without anything happening except the battery going flat

pooley124

https://www.boards.ie/discussion/comment/121453800#Comment_121453800

The only way to properly test a battery is with a load tester.

Your problem really sounds like something is draining it rather than a bad battery though. You should get a multimeter and test the current draw yourself. It's easy enough to do.

Igotadose

5.6v on it this a.m.. Tried "Noco B20 boost" - first didn't detect it, then I tried the emergency override 3 times, nothing.

Trickle charger on it now for about an hour, up to 7.6V. In another hour I'll try the Noco booster again and see if it'll turn over so I can go out and get a new battery for it.

Frustrated: Draper multimeter said '3.6v" where the trickle-charger reads 5.6v. No idea why they're different, though the draper's hooked up with the battery attached to the cables, and the trickle the cables are removed. Does that provide any hints?

pooley124

Don't think the voltage difference means anything. As I said, when the battery is charged put the car in the same state as it would be overnight, i.e everything off and doors locked, then test for current flow between the negative cable and the battery terminal.