Voltage drop for battery .
05-07-2019, 09:44 PM
#1
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Thread Starter
Voltage drop for battery .
When I turn on my car, the voltage is about 12.0V, but as soon as it cranks, it drops to 9V and then goes to 13.5V as the alternator kicks in. I drive the car about 30km/day and I just checked that voltage after driving to work 40km away. The battery should of charged to more than 12V ?
Is my battery toast? Is a 9V drop too low?
Im trying to diagnose a random ESP/ABS/ power steering/ run flat inoperable message that is popping up intermittently and wondering if it really is the battery voltage dropping too low causing this.
Is my battery toast? Is a 9V drop too low?
Im trying to diagnose a random ESP/ABS/ power steering/ run flat inoperable message that is popping up intermittently and wondering if it really is the battery voltage dropping too low causing this.
05-08-2019, 11:15 AM
#3
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2014 - W212 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
When you want to measure the car TRUE battery voltage ( not cranking ) , do not measure within short minutes of opening the door and the the hood/bonnet.
Give it up 30 minutes to allow the computers to sleep, my car will "sleep" in approx 8 minutes. Depending on car model, door opening with interior lights etc etc and computers awake may take 9 to 7 amps for few minutes
and then slowly decreasing.
The battery with this +-9 amps load can sometime drop its voltage to 12.4 from actual stand-by of 12.6 - 12.7 volts if all computers sleeping and no other loads based on near 100% state of charge.
Your 12 volts is very low though even at say 7-9 amps load. 9 volts at cranking is considered low and I hope you use the voltage MIN/MAX feature of a decent digital multimeter for higher accuracy of the
voltage sag.
How old is your battery today ?
Give it up 30 minutes to allow the computers to sleep, my car will "sleep" in approx 8 minutes. Depending on car model, door opening with interior lights etc etc and computers awake may take 9 to 7 amps for few minutes
and then slowly decreasing.
The battery with this +-9 amps load can sometime drop its voltage to 12.4 from actual stand-by of 12.6 - 12.7 volts if all computers sleeping and no other loads based on near 100% state of charge.
Your 12 volts is very low though even at say 7-9 amps load. 9 volts at cranking is considered low and I hope you use the voltage MIN/MAX feature of a decent digital multimeter for higher accuracy of the
voltage sag.
How old is your battery today ?
05-10-2019, 11:26 PM
#5
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2014 - W212 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
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zcct04 (09-04-2019)
08-23-2019, 02:25 PM
#6
Had mine tested today. 12.6 cold, with 560 CCA. Running, producing 13.6. Could this be the source of my ABS/ESP/Power-steering intermittent failure? Scheduled to get put on the Star next week...
08-23-2019, 02:40 PM
#7
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Irregular voltage has been known to upset the ESP module.
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08-23-2019, 02:41 PM
#8
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If the original battery is AGM, you should replace it with an AGM. If it wasn't (which is very possible with a 10-year old car), replace it with a regular flooded battery. AGM operates at a slightly higher voltage and has different charging characteristics, so you should use the type that your car's electrical system was designed for.
