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How to identify a poorly battery?

This is a discussion on How to identify a poorly battery? within the CLA Maintenance / Care / Detailing forums, part of the Mercedes-Benz CLA Forum category; BTW that teeny battery does not power the starter ... just keeps a few things alive during eco stops Think its only 12Ah or something ...

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Thread: How to identify a poorly battery?

  1. #21
    jmc
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    BTW that teeny battery does not power the starter ... just keeps a few things alive during eco stops
    Think its only 12Ah or something like that

  • #22
    Newbie Robuk's Avatar
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    CLA have 2 battery, 1 main for the car, and an other one for stop/start.
    So does my C-Class and my 2015 SLK 200 with tuning box, both these cars have the sensor disconnected, both batteries are now being fully charged not just to 75% as before, on the C-Class stop/start stays orange, on the SLK the light goes out, both cars have recently passed MOT`s with the sensor disconnected. According to the Honest John Web site the fuel gain between the SLK R171 and the SLK R172 is 1.9%, the R172 has Direct fuel injection, stop/start, energy regeneration and turbo which the R171 does not, all that tech for just 1.9% fuel gain, you don`t need an expensive battery on the R171 either.

    By disconnecting the sensor you will loose stop/start, energy regeneration and brake hold, The reason an expensive AGM battery is needed is to allow stop/start and regeneration to function, thats it, its also needed ifthe battery is inside the car.

    As for your constant charging method with the sensing circuit disengaged, interesting idea, though have you refilled electrolyte levels due to burn off? One can literally hear the internal bubbling at >13.6V charging levels with constant current feed. Though it seems you have been lucky
    13.6 volts WILL NOT overcharge the AGM battery neither will 14.3, do the maths. Both my Mercs charge at 14.3 volts when cars are first started, on a long drive the charge rate drops to 13.6/8 volts. The MK1 3.2 Audi TT first appeared in 2003, the battery was situated within the car and had an AGM battery, the car had a standard alternator which gave a continuous charge of between 13.8 and 14.3 volts , some of these batteries have lasted 10 years or more in the UK, this should show that a continuous charging regime of 13.8 to 14.3 volt is fine for an AGM battery.
    Last edited by Robuk; 05-13-2019 at 02:11 AM.

  • #23
    jmc
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    Well I am “hearing” things (bubbling which is an artifact of charging cant get away from that) ... at least during the initial high current stage. Then after stabilization the Ctek draws ~6.3W so considering circuit efficiencies and various losses the current is about 400mA which is about right considering all the parasitic draws these new cars have even after ignition off like constant gps reporting etc. At <0.5A and 13.7V the battery is fairly “quiet” (at least by stethoscope) so boil off is minimal.
    Guess the constant charging scheme (much like older analog cars) should work (per your real world experienced) considering the battery is not getting all of the alternator output what with all sorts of systems taking up power.

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    Veteran Geo K's Avatar
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    Quote Originally Posted by Robuk View Post
    So does my C-Class and my 2015 SLK 200 …...
    ..…
    Hi Robuk,
    Do you also own a CLA in addition to your C And an SLK? If so, which do you like the best?

    #1: '14 250 Universe Blue (Limited Ed.) + Leath, Walnut, Parktronic, Prem Pk, Interior Pk., Multimedia , Driver Assist, Lighted Sills, LoJack, Ext. War, Wheel Locks, Random Sunglasses Holder, + (Bonus - Extra Wide Door Gaps.)
    #2: '14 250 Polar Silver + [Same as above] + Pano, (Minus Random Sunglass Holder.)

  • #25
    Newbie Robuk's Avatar
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    Yes I monitor the charging system and do notice the supposedly intelligent charging system pulse charging the battery under light engine loads or coasting. In my case, despite Ctek maintenance (with proper AGM levels) whenever the car is parked at home, both times when the batteries failed it was internal plate failure ... the data showed abrupt drop from 12.5~12.6V down to <10V with key on just before ignition. So those were bad batteries unfortunately. On my 3rd one and so far it is behaving and never dropping below 11V during ignition and recovers
    This is from YUASA ,

    Undercharging

    Undercharging occurs if the battery is not receiving enough charge to return it to a full state of charge, this will slowly cause sulphation. This fault can occur if the car is being used only occasionally for short journeys, or for Start-Stop urban motoring. Undercharging will occur if alternator voltage is low (13.6-13.8volts), the alternator belt is loose or battery cables are worn and causing high resistance – If in doubt seek advice from an auto electrician.

    If your car has Stop/Start it will have smart charging and some regeneration, it is blindingly obvious that as smart charging stops the alternator from charging the battery via engine power when the battery reaches 75% SOC and there is little opportunity to charge from regeneration the battery will for long periods remain in a near to flat condition, that may have caused the two bad batteries you refer to. Before stop/start arrived I can`t remember ever discussing similar battery problems on my Audi TT forum, I have owned a MK1 since 2002 and never had an issue with batteries.

    https://www.yuasa.co.uk/info/technic...ult-diagnosis/
    Last edited by Emir; 05-15-2019 at 02:16 PM.

  • #26
    jmc
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    In my case it was faulty plates and warrantied. Seldom do short trips - have another car for that stuff. The Ctek was/is always used when parked at home. The charge energy drop rates seem to indicate >90% soc.
    But yes these electrically and electronically laden cars are tough on batteries ... even the deep cycle agms have a tough time keeping up.

  • #27
    Newbie werks400's Avatar
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    Going to give this trick a shot. Took the picture off eBay.

    Do I just disconnect this area circled in yellow and leave the electrical connector and everything else in place?

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    Thanks!


    Quote Originally Posted by Robuk View Post
    If your car has stop/start and energy regeneration this is probably the cause of shortened battery life and any low battery warning.

    The probable reason stop/start is not working is down to smart charging which does not allow the EMU controlled alternator to charge the battery via engine power beyond 75%, the other 25% space in the battery can only be filled by regeneration. If there is little regeneration on the journey the battery can remain near to flat for prolonged periods (bad for battery) and stop/start will not be activated. To test this, use a Ctech charger to fully charge battery, stop/start should then function.

    Over the last 7 months I have been running my Merc 2012 C Class petrol Coupe with the battery sensor attached to the negative lead of the main starter battery disconnected, I did this mainly to get rid of stop/start.

    With this sensor disconnected the EMU cannot read the SOC of the battery and defaults to a standard continuous charging regime of between 13.8 and 14.3 volts, this ensures the battery will now get a full charge via the alternator. With the sensor disconnected stop/start and regeneration will not function, as far as economy is concerned, this makes little difference. I have owned this Merc for 4 years and always switched stop/start off, the battery is the original and still starts the car on the first turn of the key. The odd time I have forgotten to press the stop/start button to off, stop/start has still functioned and turned to green, my Merc was registered Dec 2011, this shows its the system thats causing these flat batteries not the batteries themselves.



    Your battery was probably OK, just needed fully charging, if you buy one of these, ( https://www.ebay.co.uk/itm/UK-LED-CA...gAAOSwwPtcfmce ) you will see what I mean.

  • #28
    Newbie Robuk's Avatar
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    Hi, you just disconnect the small 2 pin black plug attached to the battery clamp. I connected my Icarsoft scanner to SLK today, the rear SAM showed 1 fault, (can`t connect to battery sensor), no other fault codes over the full scan. Car runs perfectly even with my Bluespark tuning box.
    Last edited by Robuk; 05-15-2019 at 01:17 PM.

  • #29
    Newbie werks400's Avatar
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    Will take the electrical connector off and test.

    For now charging at 14.4V~14.8V then drops to 13.1~13.4V after a while on highway. In line with what you mentioned.

    Lets see disconnecting this will bring the battery to full charge continuous.

    Thank you.

    *Update: The only error that came up via iCarsoft was U113E87: Communication with the battery sensor has a malfunction. The message is missing. Otherwise all is running well for now.
    Last edited by werks400; 05-16-2019 at 02:35 AM.

  • #30
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    How to identify a poorly battery?

    Which icarsoft unit are you folks using? I was looking at the modern versions ... any comments would be helpful

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