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So, I recently killed my last battery when it remained completely drained for 2 days at -25C. Yesterday, I replaced the battery with a new one (ok it's not new but it holds its charge fine). ''New battery'' has the same specs, 770 cca and holds 12.3-12.6V. I also confirmed that the alternator is working fine. I read 14.0V continuously.
The red battery warning light does not come off. It seems that there is no way to acknowledge the warning or reset it. Will it go off by itself ? I drived the car a few times since the replacement but it does not go away. I also tried to put the car on a battery tender overnight but still got the light.
It does not have autostart. I was wondering about the aux battery as well, but saw that some MB models will display an Aux Batt error message instead of the red battery light. Maybe I can try to measure the voltage of the aux battery as well
Maybe alternator issue , at 70000 I put in new brushes that are supposed to not wear out for 120,000 miles. It just was not charging properly. What is the voltage at rest, it should be about 12.6 - 12.8. Check both batteries.
i had large red battery warning last month. Problem was the negative cable needed replacement, there is a sensor in the wire that went bad. If your alternator is good, check if your cable went bad
Putting out 14v doesn’t mean the regulator is working to fully charge the battery, and 14.5 it should put out. Your “textbook” thoughts and not buying a new battery leave you with many possibilities of what’s wrong. Stop being cheap *** and get it all tested
Putting out 14v doesn’t mean the regulator is working to fully charge the battery, and 14.5 it should put out. Your “textbook” thoughts and not buying a new battery leave you with many possibilities of what’s wrong. Stop being cheap *** and get it all tested
You don't think an alternator putting out 14.0 volts will charge a battery completely, and that 14.5 volts is the bare minimum? Interesting concepts, those. Unique, even! ;-)
I do agree that the used battery leaves the status of one important variable unfulfilled.
No and I have proof , i got the CTEK battery monitor , it shows % charged updated continuously.
My battery is a AGM 2 years old, the new one and old one never got above 80% and sometimes went down to 30%.
The internal battery gauge and a meter showed it will go to 14.5 maybe 14.7 which is fine. So I just didn’t pay attention until one week it was around 20-40% charge . My mechanics said to replace the alternator at 6-1100.00, depending on brand.
I read up on the regulator brushes wearing out at 110000 miles. So I spent about 110$ for Fcp to send me a regulator. On the old regulator the brushes were below minimum by 1/16”. So it didn’t have good contact. With the new regulator it won’t go below 85% and often charges to 100%.
But I only have 70000 miles, so the MB brushes can wear fast in city driving with a better stereo! Few people think about changing a regulator. From what I’ve read, the alternator lasts and lasts. The regulators go bad and wear out.
I'm not sure what any of that has to do with an alternator putting out a solid 14.0 volts not being able to charge a battery. That's about the average of every car I've ever owned. Some cars with more advanced charging systems (like my BMW, not sure about my MB yet) has the option of turning down the charging voltage if it feels that's appropriate (the BMW can drop to the low 13's and be working 100.000% perfect, for example). Other "lesser cars" aren't so sophisticated, and just supply a voltage higher than the battery's fully charged voltage (mid-12's) thereby charging it.
FWIW, I have never owned a car that charges at 14.5 volts or above, and would consider that unnecessarily high, but wouldn't get my knickers in too tight a twist over it. ;-)
The MB charging system is a "smart" system similar to BMWs, VW/Audi and others. It can vary the charge level based on circuit load, battery state, engine RPM, etc.
If the battery and the alternator have checked out as "OK" I would consider it a sensor issue, and try and chase that as advised. I think at max charge you should be seeing 14.4V, at least I have, and usually see 14.2V
FYI, my battery is still the original battery from Dec 2013, so it's definitely in need of replacing. But the charging system is working flawlessly even after 129k miles. YMMV.
Inside the regulator is a circuit, mine was defective and not allowing the battery to charge to the proper amount even though the alternator was at times putting out 14.5.
The alternator itself is fine as they are well made, the regulator can be faulty in the circuit going bad, and the brushes can wear out. It’s much cheaper to replace a regulator first. Few mechanics do it this.
Inside the regulator is a circuit, mine was defective and not allowing the battery to charge to the proper amount...
I thought you said the brushes were worn beyond the minimum.
The regulator circuitry is pretty reliable. I've been dealing with solid state regulators since the 1970's and they rarely fail. Many Bosch alternators (and others as well) combine the brushes (mechanical parts) with the regulator, and when the brushes wear it's not worth the effort to change just the brushes instead of replacing the whole assembly. (I know; I've done it!)
The brushes are consumables, like brake pads.
The brushes carry the exciter current to the (rotating) rotor coils. The amount of current flowing in the rotor coils controls the amount of current, and hence the voltage, of the alternator output. Worn brushes limit that current.
Just for giggles, I just started up my (long-ignored) BMW 5-series in the garage (it's been trapped there since I got the GLK). ;-) The battery was really going soft, and was down to 11.4 volts (so nearly discharged). As expected, the BMW's (ridiculously over-engineered, over-complicated) charging circuitry allowed the alternator to go to "full power" (Scottish accent: "But cap'n, she won't take any more...") which was (coincidentally) 14.5 volts. Normally it will run at 13.5 to 13.8 volts (which is more than enough to keep my battery charged and happy).
Brushes were worn beyond minimum, and regulator for 10 years never charged good batteries above 80% . But batteries easily charged to 100% with either my Noco, or CTEK charger ! I can only think the regulator circuit was defective . I replaced the regulator and cleaned the commutator . It goes to nearly 100% now.
New battery in (790 cca) but the error message persists. I logged constant 14.1V during a 3h drive and the battery remains at 12.6V after shutting down the engine.
The voltages you report are perfect. Did you try hooking up an OBD reader to see if there is a specific error? Of course, a MB specific scanner would be even better.
Yes I tried my generic scanner and couldn't find anything useful using Torque. I haven't checked the aux battery yet. I think I will buy a specific scanner or go to the dealership. One thing I forgot to mention is that the battery light comes on as soon as I start the car (1-3 seconds after the engine is running)
03-06-2023, 03:08 PM
