1 year old battery goes from 14.5 v to 10.5 overnight

Sylvester

Sylvester

Member
Hi guys, I know there's plenty of threads about this kind of topic, but I couldn't find much info where it loses 4v overnight.

It started few days ago, suddenly no start just beeping lights, voltage shows 10.5.
I left it on charger overnight, fully charged to 14.5v. Then I put battery back, engine needed few turns but started up, no warning lights.
A day later, today, the car barely starts again, battery shows 10.5v.
Looks like I'm cycling to work again.
I know faulty ccu or other bits can drain battery, but not by 4v overnight?!
Any ideas? Thanks
 
Is the 10.5V before the starter motor is turning? ie - steady state, nothing overtly running, the battery drops 4V overnight?

I was wondering if the difficulty starting could be attributed to the starter motor earth. Ours needed cleaning 2 years ago, as it was around now when it went cold that the car went from starting reliably to literally two slow turns and instant battery death the next morning - yet would start and run fine when given a jump. Once the earth was cleaned the same battery was back to normal again, irrespective of how cold the morning was.
 
I had this happen when my alternator failed. I have Timmus DIS and when the car was running it was showing too low a voltage. It was a Saturday so I thought that I'd take it to my mechanic on Monday as with the engine off the voltage still showed over 12. The next day, the battery was 10V(ish) and I had to get the car recovered to the mechanic on the Monday and the alternator was replaced. He said battery discharge through the malfunctioning alternator was the cause.

It's all been fine for over a year since then.

I had a brand new Peugeot do the same thing back in the day...
 
Hopefully someone more knowledgeable will chip in and confirm but I think (on an AUA) the battery connects straight to the starter motor and then on to the alternator. So you should be able to disconnect the alternator at that point when you park up and then check the voltage the next morning to see if it’s stayed up. Bit of a faff but an option

Rgds

J
 
Robin_Cox said:
Is the 10.5V before the starter motor is turning? ie - steady state, nothing overtly running, the battery drops 4V overnight?

I was wondering if the difficulty starting could be attributed to the starter motor earth. Ours needed cleaning 2 years ago, as it was around now when it went cold that the car went from starting reliably to literally two slow turns and instant battery death the next morning - yet would start and run fine when given a jump. Once the earth was cleaned the same battery was back to normal again, irrespective of how cold the morning was.
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10.5v before starting the car. Yes the engine starts it's all good. If I connect the multimeter without engine on, after few minutes I can see the voltage is already dropping.
I was thinking about earth connection issue too, but I wasn't sure that could cause such drain. Which one did you have to clean? Cheers
 
birtyA2 said:
Hopefully someone more knowledgeable will chip in and confirm but I think (on an AUA) the battery connects straight to the starter motor and then on to the alternator. So you should be able to disconnect the alternator at that point when you park up and then check the voltage the next morning to see if it’s stayed up. Bit of a faff but an option

Rgds

J
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I definitely concerned it might be the alternator or the starter. There's an issue every week :/
I'll check the earthing points, then I'll have no option but check both of them too. Cheers
 
Sylvester said:
I know faulty ccu or other bits can drain battery, but not by 4v overnight?!
Click to expand...

4v overnight could be almost anything I'm afraid.

Let's start with the obvious - what exactly is the 1 year old battery that is currently fitted?
 
12v battery does not hold 14v, the initial value contains a surface charge which can be removed by turning headlights on for 10 seconds with just ignition on.
Then should be around 12.6v. I suspect you have a dead cell there's 6 in a battery all holding just over 2 volts your battery should still be under warranty.
Might be worth disconnecting battery overnight and test again
 
steve_c said:
4v overnight could be almost anything I'm afraid.

Let's start with the obvious - what exactly is the 1 year old battery that is currently fitted?
Click to expand...
It's Enduroline, I'd bought it from the website been mentioned a lot here, even used the same link. I got the battery 6 months ago, of I recall right the date on it said 2021.
 
Howey said:
12v battery does not hold 14v, the initial value contains a surface charge which can be removed by turning headlights on for 10 seconds with just ignition on.
Then should be around 12.6v. I suspect you have a dead cell there's 6 in a battery all holding just over 2 volts your battery should still be under warranty.
Might be worth disconnecting battery overnight and test again
Click to expand...
I had no issue with the battery before, all started last week when I was off work and didn't drive the A2 during that time.
Yes I plan do that, I'll charge it up again, and take it out for 3 days to see if it loses the charge.
If that doesn't help I'll start removing the fuses 1 by 1, then probably the next step will be a new CCU :/
Its gonna be great as well cycling in the rain at 5am.
 
birtyA2 said:
I recently posted the following

Removing the starter motor on an Audi A2 1.4 AUA

This article covers the removal of the starter motor from the A2 1.4 AUA petrol and is probably relevant for the later BBY as well
www.a2oc.net www.a2oc.net

The picture on page 5 shows one earth you could look at

J
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Thanks for the link.
That's interesting, as the same earthing point got loosened up during new clutch fitting, and the cable got in the way of the balancer weight, which caused miss-shifts for weeks. I found this out when the balancer already was touching the metal cable underneath.
I'd patched that up, moved it out the way, and hasn't caused any issues since. But I'll have a look tomorrow before work, just to be sure. Cheers
 
Sylvester said:
I had no issue with the battery before, all started last week when I was off work and didn't drive the A2 during that time.
Yes I plan do that, I'll charge it up again, and take it out for 3 days to see if it loses the charge.
If that doesn't help I'll start removing the fuses 1 by 1, then probably the next step will be a new CCU :/
Its gonna be great as well cycling in the rain at 5am.
Click to expand...
If the battery retains charge when disconnected from the car then you could just do that while you use it until you have more time to investigate the issue. Simply drive it , then when parked up, remove the battery earth lead. Refit when you need to drive.
Of course you will need to ensure that you can access the car using your key in the driver's door, and whilst disconnected the boot won't unlatch with the handle, so you will need to get to the battery via the rear seats.
It's a hassle, but keeps you out of the rain!
 
Catnip64 said:
If the battery retains charge when disconnected from the car then you could just do that while you use it until you have more time to investigate the issue. Simply drive it , then when parked up, remove the battery earth lead. Refit when you need to drive.
Of course you will need to ensure that you can access the car using your key in the driver's door, and whilst disconnected the boot won't unlatch with the handle, so you will need to get to the battery via the rear seats.
It's a hassle, but keeps you out of the rain!
Click to expand...
That's a good idea, I actually did that when I went on summer holiday. Removing the earth had triggered the alarm, but only until using the key. Thanks Catnip.
 
Howey said:
12v battery does not hold 14v, the initial value contains a surface charge which can be removed by turning headlights on for 10 seconds with just ignition on.
Then should be around 12.6v. I suspect you have a dead cell there's 6 in a battery all holding just over 2 volts your battery should still be under warranty.
Might be worth disconnecting battery overnight and test again
Click to expand...

Taking the 12.6V figure for all 6 cells. If you divide 12.6V by 6 you get 2.1V per cell.

Now 5 cells x 2.1V = 10.5V which is the voltage that you are getting after the car has been left a while.

This suggests that one of the cells has gone completely bad and quickly goes down to zero Volts.

If the Voltage doesn't keep going down further than 10.5V then it sounds like you need a new battery.

If there was a very big drain on the battery, you would expect the Voltage to keep going down and not stabilise at 10.5V.

However, I would have removed the Earth lead and charged up the battery. Then left it overnight and checked the Voltage in the morning. If the Voltage was much below 12.6V (with the Earth lead still removed) then the battery has gone bad (or at least one of the cells) and needs replacing.
 
carlston said:
If the Voltage doesn't keep going down further than 10.5V then it sounds like you need a new battery.

If there was a very big drain on the battery, you would expect the Voltage to keep going down and not stabilise at 10.5V.
Click to expand...
I've checked it before work and the voltage had gone down to 9.5v.
I've taken the battery out and gonna recharge it tomorrow, but I got a feeling the culprit gonna be the CCU.
 
Have you tested for a parasitic drain?

Eric the car guy is awesome on YouTube at explaining the process
 
Howey said:
Have you tested for a parasitic drain?

Eric the car guy is awesome on YouTube at explaining the process
Click to expand...
Yes I'd seen that video, he's a cool guy. If i recall it right, he was explaining similar what others have mentioned here as well, that it can be checked by removing the fuses 1 by 1 and when the voltage drops, that's the issue. I'm gonna check that on the weekend, if the battery holds the charger when it's out of the car. Cheers
 
So this interesting thing has happened. I took the battery out and left it uncharged for a day. 2 days ago showed 10.5v, yesterday 9.5v.
So when I was about to put it on charge today, I've check the voltage and it showed 12.3v.
Charger showed 40%, then quickly to 60% and charging slowly now.
I know voltage can bounce a bit, but +3v seems rather big jump. Also 1 hour later it's already on 80%.
Either way, I'll leave it out of the car for few day and see how does it hold the charge.
 
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