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I have this odd issue, when I sit in the car with the engine running and with the windows up, if I flick both switches up to indicate closing. The voltage of the car will drop from 14.1 to 13.8 and as low as 13.3 and the lights on the dash will flicker/dim as well as an rpm surge of say about 100 rpm.
This does not happen with normal window operation. Only the above.
Is this signs of a failing alternator? voltage regulator or battery?
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
I only heard clicking. Didn't see what you were talking about.
IF you try to raise the windows when they are already up, there is a big draw on the alternator. Is this something new that has developed or did you not notice it before? How long has it been happening?
I see the dimming, quite noticeable, but I have never really noticed the dimming my car so will look. The voltage should sit around 14.1V and dip down with rear heater and windows etc, the voltage regulator will then so its job to regulate the voltage. So long as your car is putting out 14.1 V then your car alternator is okay. I will check my car an see.
I only heard clicking. Didn't see what you were talking about.
IF you try to raise the windows when they are already up, there is a big draw on the alternator. Is this something new that has developed or did you not notice it before? How long has it been happening?
Notice the illuminated lights dimming. Ok, I guess that makes sense. I recently noticed it when I hit the window button in the wrong direction.
Originally Posted by A1EK
I see the dimming, quite noticeable, but I have never really noticed the dimming my car so will look. The voltage should sit around 14.1V and dip down with rear heater and windows etc, the voltage regulator will then so its job to regulate the voltage. So long as your car is putting out 14.1 V then your car alternator is okay. I will check my car an see.
@Das Geld 2 I noticed this for the first time a few days ago.
Troubleshooting led me to discover that the rear / consumer battery was in very bad shape.
No warnings, just some odd quirks with the car. Removed the battery and it took a full charge without issue, but when tested, showed 6% health remaining.
New H6 AGM went in and all of those quirks I was noticing went away.
There still is a slight flicker when holding both window switches up past closed, only noticeable if looking for it. I'll take this as normal operation if both batteries are now perfect and the car is showing a steady 14.1 - 14.3 V while running.
Check that consumer. I was surprised it could be that bad without throwing all kinds of warnings / errors.
@Das Geld 2 I noticed this for the first time a few days ago.
Troubleshooting led me to discover that the rear / consumer battery was in very bad shape.
No warnings, just some odd quirks with the car. Removed the battery and it took a full charge without issue, but when tested, showed 6% health remaining.
New H6 AGM went in and all of those quirks I was noticing went away.
There still is a slight flicker when holding both window switches up past closed, only noticeable if looking for it. I'll take this as normal operation if both batteries are now perfect and the car is showing a steady 14.1 - 14.3 V while running.
Check that consumer. I was surprised it could be that bad without throwing all kinds of warnings / errors.
Thanks H!
Good to know, I keep mine on a CTEK year round.
I am planning to get new batteries for the upcoming spring season.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by Das Geld 2
Which brand did you go with? Optima?
Many people have posted that the battery from the dealer is competitive with the auto parts store. But, before reading that, I got mine from FCP.
(NOTE: These are batteries for my 2015 SL400. Those prices were from 2022, just two years ago. Today's prices for the big one is nearly $100 more! Inflation? Nah, it's under control.)
I am planning to get new batteries for the upcoming spring season.
Which brand did you go with? Optima?
Anytime!
I went with a Duralast Platinum H6 AGM. Meets the exact factory specs and is available at a local AutoZone.
OE Genuine wasn't that much more expensive, but the warranty on the Duralast is better / easier to deal with.
@JettaRed Considered that Odyssey option (I've used their batteries before and liked them) but decided against it after realizing the specs are off from factory (720 vs. 760 CCA and 69 vs. 70 Ah).
I realize it's only slightly off, but given the BCM and general complexity / sensitivity of the electrical system, I just didn't want to deviate from factory spec in any way.
I have this odd issue, when I sit in the car with the engine running and with the windows up, if I flick both switches up to indicate closing CBT test training in Milton Keynes. The voltage of the car will drop from 14.1 to 13.8 and as low as 13.3 and the lights on the dash will flicker/dim as well as an rpm surge of say about 100 rpm.
This does not happen with normal window operation. Only the above.
Is this signs of a failing alternator? voltage regulator or battery?
A voltage drop from 14.1V to 13.3V when holding both window switches up suggests a high electrical load. It could be a weak battery, failing voltage regulator, or poor grounding. If the alternator isn’t compensating properly, it might be struggling. Check battery health, alternator output under load (should stay above 13V), and grounding connections for corrosion.
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