Dead Car Battery?

Discussion in 'Automotive Electronics' started by ISB123, Jan 19, 2016.

  1. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Hello,it seems that my battery is out of charge since I can't start the car. I measured the voltage of 12.3V at the battery terminals, when electronics are on voltage drops to around 11V and when starter motor is cranking to around 8V. I'm currently trying to recharge it but I'm not sure if it's even accepting a charge since only after few minutes it drops from 6A to what it seems to be 1A on the gauge. Battery is Energizer EM72-LB3.
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    It should not drop to 8 volts when powering the starter.
    If you measure it after charging, you should see over 13 volts. When systems are on (lights, radio etc.) It should read 12.6 volts.
    Showing 12.3 after a full charge means you have one shorted cell in the battery.
    If it is a wet cell battery with caps. You can pour out the acid and rinse the cells out with distilled water, the refill the cells with acid you poured out. That may remove the short if caused by sediment. If the plates are warped and touching or it is SLA type then best use of your time would be buying a new one
     
  3. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    If the cells were shorted, they wouldn't see 12.3V unloaded. There are six cells in the 12 volt battery charged to 2.1 volts at full charge. I suspect the internal resistance of the SLA has increased causing the excessive IR drop under load.

    Visit Battery University for more info.
     
    Last edited: Jan 19, 2016
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  4. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    I checked the voltage while its charging and its reading 15V but ammeter shows almost 0A.
     
  5. JoeJester

    AAC Fanatic!

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    That's not a complete circuit ... of course, your smallest meter reading could be in the 100s of milliamperes.

    On edit: added battery voltage test
     
    Last edited: Jan 19, 2016
  6. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    How? If Current drops in 15minutes from 6ish A to almost zero.
     
  7. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Your battery is monitoring the "charge" via the battery voltage. I responded earlier too quickly, before I created the example.

    If your "dead" battery has a higher internal resistance, the 6 ampere charge will start charging the battery, and as the battery charges, with a constant internal resistance, the voltage at the battery terminals will increase to 13.8 volts quickly and the charger will shift to the trickle or a lower charge rate. That is what you are seeing.
     
  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Yes. The battery will read 13.8 volts for quite some time after being disconnected. IF it has 6 good cells.
    Under a light load it should read 12.5 to 12.8 volts.

    If it reads 11 volts under a light load ... you have a shorted cell.

    Do not confuse the higher voltage reading seen right after charging with a proper voltage reading taken under a slight load. The load quickly drains the excess surface charge and shows the true voltage values.

    Charge the battery and leave it disconnected for a full 24 hours. That 12.3 volt reading will drop down to about 10.8 or so.
     
  9. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Thanks for the help guys I will check if its working tomorrow after charging.
     
  10. cork_ie

    Member

    Oct 8, 2011
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    If your battery is measuring 12.3V no load and off charge ( more than an hour since it was last charged) then it is approximately 70% charged.
    If your voltage is dropping to 11V with ignition on and 8V cranking , then your battery is in very poor condition and you should change it before you do damage. If you get any kind of a rotten egg smell or if the battery is fizzing in one cell when cranking, it is definitely dead .
    It is a fairly standard 72Ah battery with a CCA of about 650A. I expect you should be able to buy a replacement or about €65-70 without too much trouble.
     
    Last edited: Jan 19, 2016
  11. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Well after charging for few hours the voltage now is actually 12V so I'm just going to buy a new one and send it to mechanic to check the alternator.
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    If you are charging the battery while still connected in the car, you could have high corrosion between the terminals (posts) and cables. It may not be visible until you remove the cables. Measure right at posts and do not connect the charger to the cables. Of course, it is better to remove the cables, clean the terminals then charge.

    If you have removed cables, then it is time for a new battery.
     
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  13. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Those auto chargers sense the voltage at the battery terminals and reduce the charging current to a lower value when the battery terminals read a higher voltage. Below is and example ...

    6 amps through 90 milliohms produces an IR drop of 0.54 volts. The DMM reads the battery voltage plus the IR drop across the internal resistance. 13.14 volts.
     
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  14. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Hello, just bought a new battery.Car now starts barely it seems that glowplugs are almost dead and alternator is working fishy. Battery measured 12.65V which is fine but alternator measures 13.5V when car is at idle and 13.3V when at 2000RPM. So something is definitely wrong.
     
  15. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Is that battery measurement (12.65) with motor running? If so sounds like you have a cable/connector problem.
    What indicators are you using t say the glow plugs are almost dead?
    edit: what type of vehicle?
     
  16. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Battery is measured when motor is not running.It's a diesel car,I think that glow plugs are almost dead because the glow plug light stays on for very long time and still doesnt heat the engine enough to start it at low temperatures.Now I have to run the heating cycle 3-4 times and crank the engine for 10-20sec. to start it.
     
  17. crutschow

    Expert

    Mar 14, 2008
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    I once replaced an alternator I thought was bad, but the problem turned out to be a slipping belt.
     
  18. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    @ISB123

    If you have any reason whatever to suspect the battery - please just replace it! -- A battery 'going high-Z' during operation of the engine (and, hence, the charging system) will likely result in destruction of every electronic component on the vehicle!:eek: -- very annoying!!!:mad::mad::mad:

    Best regards and good luck!
    HP:)
     
  19. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    If your charging system regulator is out of whack it could be the cause of the low charging voltage you see with engine running.
     
  20. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Could be that too.Car is going to mechanic tomorrow so I will see whats up with the car in few days.
     
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