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  1. Re: Low battery warning 
    #11
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    Yes I know, but the vehicle charging system is still a battery charger... so where I've said "sceptical that a charger could..." replace with "sceptcal that a charging system, whether internal or external, could...".
     
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  2. Re: Low battery warning 
    #12
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    I believe the charging system in the latest models is fairly intelligent thus the need to recode a new battery but I could be wrong
     
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  3. Re: Low battery warning 
    #13
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    I may well be wrong, I'm just sceptical that it's possible to build in intelligence that means the system doesn't need some battery parameters in order to charge it both optimally and safely. Specifically it's post #7 that I'm commenting on. AGM and conventional lead-acid have quite different optimal charging voltages, charging a conventional lead acid battery as though it were AGM could lead to gassing (which with a sealed battery could lead to it exploding). Anyway all I've done is thrown in some doubt so I'll leave it there.
     
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  4. Re: Low battery warning 
    #14
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    Had this issue a few times over lockdown. Car is only driven once a week on average and twice after cold spells it wouldn't start. After recharging it was all OK. Checked with VW and batteries are guaranteed for 5 years (mine is 3.5 years old). They kept the car plugged overnight, did a battery test and it came back "battery good". I think I will bite the bullet and get a new battery sooner rather than later. Can the battery be recoded using OBDeleven?
     
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  5. Re: Low battery warning 
    #15
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    ok, so this is what you need to know, covid has affected a few batteries due to cars not being used. if you have a modern charger that charges an AGM battery properly put it on for 24 hours and it should be fine and pick up. If you decide you need one,
    A: you dont need a radio code,
    B: you only need worry about reconfiguring a new battery if it a different spec.
    C: even if it is a different spec - if its a bigger spec it wont hurt the new battery, it just wont charge it up to full capacity. If its a smaller spec - you need to or it will over charge very quickly and kill your new battery.
    D: you can configure it with VAG COM OR OBDELEVEN.
     
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  6. Re: Low battery warning 
    #16
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    That's useful. Just a minor quibble, " if its a bigger spec it wont hurt the new battery, it just wont charge it up to full capacity" - the best way to damage a lead acid battery is to regularly fail to fully charge it. In this instance I suspect that all will happen is its capacity will gradually reduce to the meet what the charger is expecting so no real harm done.

    I have suspicions about the state of the battery in my Dec '19 Passat. A couple of weeks a ago I had a week of lots of driving (a couple of 200+ mile runs, and 20-40 most other days), then a week later the car refused to start because the battery was too low. Jump started it and went for a drive, 10 mins later tried to restart it - refused. Jump started it again to get it home (battery was at 11.8V, not good) and then put the battery charger on for 24 hours after which it started. I've always had suspicions because unlike the previous 2 Passats, where the stop-start system stopped the engine almost every time you came to a stop, on this one it hardly ever stops it - even after a 4 hour daylight drive with no air-con etc. you can come to a stop and the A symbol on the dash has the line through it meaning that it doesn't want to do it for some reason (e.g. battery too low). On the very rare occasion that it does stop the engine it generally restarts it after anywhere between 5 and 15 seconds. Maybe the battery has always been slightly dodgy.

    Car is still under warranty so it's booked in to a VW dealer for a battery test next week.
     
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  7. Re: Low battery warning 
    #17
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    Mike, an AGM isn't a lead acid battery.....
    The other thing is it charges differently, even when fully charged it will only show about 12.6. Question. When did it start normally? After it was trickle charged? You may have an alternator/charging problem rather than a battery problem
     
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  8. Re: Low battery warning 
    #18
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    AGM IS a lead acid battery but with major improvements over the older batteries. As with many advances in technology they were developed by the military in the 1980s.
     
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  9. Re: Low battery warning 
    #19
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    Quote Originally Posted by user name View Post
    Mike, an AGM isn't a lead acid battery.....
    Oh yes it is ... it's not a 'wet' cell lead acid battery, but it is lead acid. The acid is Absorbed in a Glass Mat, the plates are lead. AGM batteries have a lower internal resistance and hence will charge a lot faster (draw a higher charge current for a given applied voltage). I use AGM batteries as leisure batteries on a boat for that very reason (though they stay at around 13V for a long time after a full charge, and only decay to around 12.8V after the surface charge has dissipated).

    Useful info here on different types of batteries and absorption/float charge voltages: 5 Battery Types Explained - Sealed, AGM, Gel | BatteryStuff

    Question. When did it start normally? After it was trickle charged? You may have an alternator/charging problem rather than a battery problem
    Yes after a day on the charger it started OK. I had the same thought as you about a charging problem. When the battery was down at 11.8V I monitored the voltage with the engine running after a jump start (jump battery now disconnected), it was showing around 12.5-12.6V (more revs made no difference) which is nowhere near enough to properly charge the battery - so that point I did suspect the alternator/charging system. However after charging the battery and starting the engine from it unassisted the voltage with the engine running was showing 14.8. I wonder whether the charging system has some intelligence built in such that if the battery is really low it does some sort of soft-start on the charging, and I just didn't monitor it for long enough when it was showing 12.6V.

    I'm going to monitor the battery voltage over the next couple of days and see if it drops significantly when the car is sitting unused.
     
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  10. Re: Low battery warning 
    #20
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    If you want to picky you will find it was developed FOR the military it will be a cold day in hell when the military starts inventing batteries. I was trying to point out they are different that's all. Alternator charging should be around 14.4 so if your car Alternator is only charging at 12.6 you have your culprit.
     
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