Battery Charging Questions
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Battery Charging Questions
Hi,
I just noticed that my car is only charging the battery to above 13.8 V when the AC fan is turn to Max. Under no load or no AC fan at Max, the car is charging at 12.5v/12.6v. Right after I turn on the engine, sometimes the volt increases 13.8, but shortly drop to 12.5v/12.6v. Check serpentine belt and pulley and they look fine. I did have one start issue and solved after I charged the battery (the battery is only 1 year old).
My questions:
- Does the car should always charge at 13.8v ish when the engine is on?
- Do I have a weak alternator issue?
The car is 2010 and has 100,000 km.
Thanks,
I just noticed that my car is only charging the battery to above 13.8 V when the AC fan is turn to Max. Under no load or no AC fan at Max, the car is charging at 12.5v/12.6v. Right after I turn on the engine, sometimes the volt increases 13.8, but shortly drop to 12.5v/12.6v. Check serpentine belt and pulley and they look fine. I did have one start issue and solved after I charged the battery (the battery is only 1 year old).
My questions:
- Does the car should always charge at 13.8v ish when the engine is on?
- Do I have a weak alternator issue?
The car is 2010 and has 100,000 km.
Thanks,
Member
Joined: May 2010
Posts: 138
Likes: 16
2010 E350 Luxury 4Matic
Hi,
I just noticed that my car is only charging the battery to above 13.8 V when the AC fan is turn to Max. Under no load or no AC fan at Max, the car is charging at 12.5v/12.6v. Right after I turn on the engine, sometimes the volt increases 13.8, but shortly drop to 12.5v/12.6v. Check serpentine belt and pulley and they look fine. I did have one start issue and solved after I charged the battery (the battery is only 1 year old).
My questions:
- Does the car should always charge at 13.8v ish when the engine is on?
- Do I have a weak alternator issue?
The car is 2010 and has 100,000 km.
Thanks,
I just noticed that my car is only charging the battery to above 13.8 V when the AC fan is turn to Max. Under no load or no AC fan at Max, the car is charging at 12.5v/12.6v. Right after I turn on the engine, sometimes the volt increases 13.8, but shortly drop to 12.5v/12.6v. Check serpentine belt and pulley and they look fine. I did have one start issue and solved after I charged the battery (the battery is only 1 year old).
My questions:
- Does the car should always charge at 13.8v ish when the engine is on?
- Do I have a weak alternator issue?
The car is 2010 and has 100,000 km.
Thanks,
I too have a 2010.
Few years back i was chasing a power issue. I was experiencing weak starts - slow to turnover. Low starting battery voltage < 12V in the morning. In my reserach in forums, I believe the alternator is not always charging the battery when on - due to its programming/efficiency. I was hoping that it was just a weak battery, so i replaced the battery due to oringial battery age (7 years) . But with new battery, starting voltage was still low after few days sitting. I didn't think i had any parasitic drain. I took the car to independent shop in and they determined that the alternator was "inconsistent" and recommended replacement, gave me choice of lower cost remanufactured or new Bosch with lifetime warantee. The latters cost me about $900. The problem is gone after alternator was replaced.
I've also bought a Costco battery tender to plug in in the winter months if its not going to be driven for weeks. I watched FCP Euro video with their Mercedes brand manager Kyle, he said one of the quickest ways to kill an alternator is to put in a weak battery because of the stress it causes.
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Hi,
I just noticed that my car is only charging the battery to above 13.8 V when the AC fan is turn to Max. Under no load or no AC fan at Max, the car is charging at 12.5v/12.6v. Right after I turn on the engine, sometimes the volt increases 13.8, but shortly drop to 12.5v/12.6v. Check serpentine belt and pulley and they look fine. I did have one start issue and solved after I charged the battery (the battery is only 1 year old).
My questions:
- Does the car should always charge at 13.8v ish when the engine is on?
- Do I have a weak alternator issue?
The car is 2010 and has 100,000 km.
Thanks,
I just noticed that my car is only charging the battery to above 13.8 V when the AC fan is turn to Max. Under no load or no AC fan at Max, the car is charging at 12.5v/12.6v. Right after I turn on the engine, sometimes the volt increases 13.8, but shortly drop to 12.5v/12.6v. Check serpentine belt and pulley and they look fine. I did have one start issue and solved after I charged the battery (the battery is only 1 year old).
My questions:
- Does the car should always charge at 13.8v ish when the engine is on?
- Do I have a weak alternator issue?
The car is 2010 and has 100,000 km.
Thanks,
The alternator output is controlled by the engine computer. When the battery is recognized being full then the voltage is switched to a 12.6V float voltage only. This prevents overcharging AGM lead-acid battery and saves pennies in gas.
What you never want to see is voltages below 12.3, 12.1, 11.9, 11.6... with engine running.
Use a CTEK float charger to prevent SAM vampires from draining battery while unused.
Disconnecting battery is also an excellent practice to "Reboot car computers" (car may have aux batt).
Having a healthy alternator/battery voltage prevents many glitches from materializing into faults.
Enjoy your ownership !
Last edited by CaliBenzDriver; Aug 26, 2022 at 04:27 PM.
