VW Passat - Do I need to Replace Battery?

Honest John Back Room » Technical matters
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Mon 4 Jan 2021 08:47
VW Passat - Do I need to Replace Battery? - ap87

Hi all, so i've been working from home for a few months now so not using the car as much, just the odd trip to the shop and back, nothing more than 15-20 minutes. I then went to start it over the weekend after a couple of days in the freezing cold and although it started first time, it chugged a little bit and took a good few seconds to finally start.

I checked voltage of the battery the next morning after sitting all day and it was 11.8 at the time and then when starting the car the cranking voltage dropped to around 9 then back up to over 14.

Is it just the cold thats not helping here and if I take it out for a proper driveevery now and then, can I still live with this battery for many more months to come if I keep an eye on it?

Its a stop start model so you are looking at £150+ for a new battery, something I could do without buying at the moment unless really needed.

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Mon 4 Jan 2021 09:01
VW Passat - Do I need to Replace Battery? - RT

It'll be a combination of reduced usage and the cold weather - get yourself a decent smart charger, eg CTEK MXS 3.8 or CTEK MXS 5.0 and charge it for 24 hours once a month - cheaper than a new battery and will last much longer.

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Mon 4 Jan 2021 11:41
VW Passat - Do I need to Replace Battery? - edlithgow

It'll be a combination of reduced usage and the cold weather - get yourself a decent smart charger, eg CTEK MXS 3.8 or CTEK MXS 5.0 and charge it for 24 hours once a month - cheaper than a new battery and will last much longer.

IF you have to choose one of them, the 3.8 is perhaps a better bet.

There are plausible (IMO) reports of corner cutting on the CTEK MXS 5.0, though they might have fixed it by now.

www.youtube.com/watch?v=xeTJTzKRUy0

Discussion near the end of this thread

www.honestjohn.co.uk/forum/post/137525/battery-cha...r--

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Fri 8 Jan 2021 11:50
VW Passat - Do I need to Replace Battery? - edlithgow

It'll be a combination of reduced usage and the cold weather - get yourself a decent smart charger, eg CTEK MXS 3.8 or CTEK MXS 5.0 and charge it for 24 hours once a month - cheaper than a new battery and will last much longer.

If you want an expensive Chinese charger the Noco Genius 5 looks not bad, and explicitly addresses the dead battery issue with "Force Mode" which will charge a battery with no voltage.(I've been calling that "dumb mode" which I suppose might not sell so well)

Mr Smoke has just started looking at it, and, although he thinks it is overpriced, he doesn't so far seem to think its junk like the CTEK 5 amp

www.youtube.com/watch?v=yZPg34fwU0Q

A look inside (2 amp model)

www.youtube.com/watch?v=22NUiDW6j18

On test rig

www.youtube.com/watch?v=yhYYZB7iukE

Edited by edlithgow on 08/01/2021 at 12:56

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Mon 4 Jan 2021 09:22
VW Passat - Do I need to Replace Battery? - Andrew-T

You don't say how old it is. The working life of a battery is unpredictable, anything between 5 and 12 years depending on usage and whether petrol or diesel. But the immediate reason is the cold spell, plus the continuous drain by the electronics in an idle car. Probably better to trickle charge rather than using fuel on a 'proper drive' at intervals.

Edited by Andrew-T on 04/01/2021 at 09:24

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Mon 4 Jan 2021 09:29
VW Passat - Do I need to Replace Battery? - ap87

The car has just turned 9 years old but i've only had it for 2 years so I dont know how old the battery is

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Mon 4 Jan 2021 09:40
VW Passat - Do I need to Replace Battery? - elekie&a/c doctor
It could be the original battery . If it is , then it needs replacement. Check the top of the battery to see if there are any date stamps .
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Mon 4 Jan 2021 11:43
VW Passat - Do I need to Replace Battery? - John F
It could be the original battery . If it is , then it needs replacement.

Why?

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Mon 4 Jan 2021 12:38
VW Passat - Do I need to Replace Battery? - Andrew-T
It could be the original battery . If it is , then it needs replacement. --- Why?

John, you are being a bit disingenuous. Perhaps Elekie should have included the word 'probably'. Most 9-year-old batteries are no longer in the flush of youth, and quite a few will have already expired. But I agree that this one will certainly need charging, given the circumstances.

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Mon 4 Jan 2021 13:45
VW Passat - Do I need to Replace Battery? - Railroad.

If the car is less than about 10 years old then you can't just easily replace the battery. It will have a Battery Energy Management system on it (module 61, Battery Regulation). You will need to get an OEM battery and enter the battery type and serial number using suitable diagnostic equipment into the module so that the vehicle systems can correctly utilise the battery. You will see a sticker on the battery with this information, and you will have problems if you don't do it.

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Mon 4 Jan 2021 14:07
VW Passat - Do I need to Replace Battery? - RT

If the car is less than about 10 years old then you can't just easily replace the battery. It will have a Battery Energy Management system on it (module 61, Battery Regulation). You will need to get an OEM battery and enter the battery type and serial number using suitable diagnostic equipment into the module so that the vehicle systems can correctly utilise the battery. You will see a sticker on the battery with this information, and you will have problems if you don't do it.

You don't need an OEM battery or a BEM sticker! Just changing the old serial number by one digit is enough to tell the BEM that a new battery is fitted.

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Tue 5 Jan 2021 15:43
VW Passat - Do I need to Replace Battery? - BPL

Try the CTEK or equivalent on recondition / recondition mode overnight until it finishes. Don't let the battery go under 12V without recharging. You may have a ghost drain, you can use an ammeter and pull fuses until you find it but its not easy as all the doors closed and bonnet will have to be down so the computer and alarm can go to standby, this may take a minute each time.

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Fri 8 Jan 2021 11:08
VW Passat - Do I need to Replace Battery? - edlithgow

Try the CTEK or equivalent on recondition / recondition mode overnight until it finishes. Don't let the battery go under 12V without recharging. You may have a ghost drain, you can use an ammeter and pull fuses until you find it but its not easy as all the doors closed and bonnet will have to be down so the computer and alarm can go to standby, this may take a minute each time.

My understanding is fuse-pulling may no longer work on a newfangled car because it upsets the computer system(s), triggering a cascade of enhanced drain until it settles, which may take a lot more than a minute,

I believe the advised method is to clamp door, etc switches to spoof them closed, and then measure the voltage drop (which will be a few millivolts) across the fuses with a multimeter.

This is theory, I have no experience of it, since so far I've been able to avoid machines with such ghosts in them..

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