When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
My car has a weird issue with the additionnal battery:
-obviously the car prompts the additionnal battery fault 30sec after starting the engine
-battery has 12,8V (tested at home and at a local battery shop, it passes the test on their testing device with no problem)
-when I start the car and mesure the battery voltage it shows 14,8V then after 20-30sec it drops to 12,8V and the error appears
I am wondering what can be the issue, as the battery looks ok
May it be the battery controller which is on the battery left side (A 000 982 2023) ? or something else ?
Should I take the risk and buy the battery anyway ? Or buy this controller, it looks quite cheap ?
PS: i have access to xentry, but it didnt show anything beside battery fault
Thanks for your help,
Peter
Last edited by divepopo; Jun 18, 2021 at 07:48 AM.
The kludge hanging on the battery side is not a battery controller, it's just a solid state switch ("relay") to connect/disconnect AUX from the main circuit. The control is operated by the SAM's.
Dirty AUX GND !
You can check the contact cleanliness at (+) & (-) battery poles and also the AUX ground point to chassis shown above. Is yours good enough to pass 50Amps from AUX without too much drop?
This GND point is nearly as essential as main battery GND or chassis/engine GND strap.
Last edited by CaliBenzDriver; Jun 18, 2021 at 08:06 PM.
Batteries can be faulty because of improper internal resistance. Nistbattery testers will not tell you what this is. Also, when you drive, you are constantly (potentially) charging your aux battery so the voltage may not look low when you test it with a voltmeter. I believe most Walmarts have fairly sophisticated battery testers. Might check with them.
I wonder, does MB inside its rear SAM actually has equivalent circuits/capability like a Midtronic battery tester where the internal resistance of the batttery is measured and deemed GOOD/BAD from there.
I read it is not a simple as Ohms reading, but the Midtronic Battery Tester send special pulses to the battery.
Midtronics testers measure the conductance as an AC function. Impedance meters use a pulsed load and calculate the resistance based on the step change in the current when the load is pulsed. Conductance is also an AC test. https://www.sbsbattery.com/PDFs/Cond...erySystems.pdf http://www.skylark.co.uk/CONDUCTANCEQ-A.htm
If I read correct, even in WIS/EPC, Midtronic is the approved battery tester for MB.
I Remembered during my charging test, there will be a time after engine start that 10 or so seconds, will be zero charging and that is when the rear baby aux battery 12Ah is being measured ( I am assuming ),
as it has to be removed from the main alternator charging circuit.
I think they figure the battery equivalent internal resistance by watching the voltage drop over a period under a measured current load.This gives a straight slope between two points such as y = Ax + B
where A would be the resistance.
(schooling memories from decades ago)
The current is communicated once either by Hyundai before disconnect or the Alternator then the two battery MOSFET relays (inside PreFuse + AUX side) are actuated to switch MAIN= OFF & AUX= ON to observe the voltage going down supplying the known load.
This is the same setup that's used during ECO Restart when 100% of MAIN goes to starter and AUX powers the whole car minus starter.
Oxidized connection points will make AUX appear worse than it really is.
Last edited by CaliBenzDriver; Jun 21, 2021 at 12:35 AM.
First thing I did was cleaning the battery terminals and the ground (same as on the picture), the + on the battery was very oxydated, but cleaning it did not resolve the issue.
I will order a new battery, do you think I should buy one from the dealer or a replacement with same parameters 12V / 200amp will be as good ?
Last edited by divepopo; Jun 21, 2021 at 08:33 AM.
First thing I did was cleaning the battery terminals and the ground (same as on the picture), the + on the battery was very oxydated, but cleaning it did not resolve the issue.
I will order a new battery, do you think I should buy one from the dealer or a replacement with same parameters 12V / 200amp will be as good ?
I'd say the OEM part will give you peace of mind at a reasonable cost. It's the most compatible part.
That mid size battery needs to keep your car reliably powered while the engine is restarting from a Stop sign. You don't want to ghost in the middle of an intersection .
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
