So I have a Voltphreaks VPH750 lithium battery. I like it. It has discharge protection that shuts off the battery whenever it runs down to a level needed to start the car. So while I come back to a dead car every couple of drives, all I have to do is turn the battery back on and the car will start right up. So far so good. Here are the specs:



I’ve had my car back on the road for a couple of weeks now, and took my first long drive yesterday, ~200mi up to Paso Robles and back. Car is like a go kart now, but not much fun to drive that distance anymore, and I possibly carbon monoxide poisoned myself - a story for another time.

When I got up to the AMG meeting point at Paso Robles and shut the car off, the discharge protection kicked in immediately. Strange. When I left, just turned the battery on and she fired right up. Ok.

Early into the drive home, I got the big red dead battery indicator on the dash and knew I had a problem. Had my OBD2 dongle in, so checked the voltage - cruising steady at 80mph battery voltage was showing 11.5-12.5 volts. Shut off the radio and lights, didn’t seem to make a difference but I got home. As soon as I parked and shut the car down, discharge protection kicked in immediately. (it fired right up this morning after switching the battery on)

Now if I recall how the charging system works, my voltage while running should be 14V. And battery size or capacity should have no bearing on this. So I’m wondering what’s going on here. On a long drive like that, the battery should be super charged up, not slowly draining as I drive along. Do I have something drawing excess power while running, a bad alternator, or could this be battery related? I just moved the battery and wires and fuses around so maybe I have a short or something back there, that’s what I’ll check first today.

Anyone want to venture a guess?

 

Most likely the voltage regulator on the alternator is wearing to a point where it's not charging well.

You don't need a new alternator and most likely the brushes on the regulator.

I had a similar issue with a new bosch battery and it ended up being the battery. I was seeing 14 volts with car running and the battery would die over night and not start the car in the summer.

 

Well that’s a good place to start, thanks. What’s the process for replacing that regulator?

 

Yes the regulator would be my first guess. Battery size shouldn’t matter like you said I have an even smaller battery and everything is good. What I noticed is if the cables on the battery are not super tight and clean it doesn’t charge like it would normally with a larger capacity battery for whatever reason

 

That’s a good point too. I just noticed that my negative battery terminal is loose and not screwed in completely. I’ll start there.

Can the voltage regulator be purchased separately? I imagine it’s connected to the alternator and can be just popped off? Anyone have a part number? Thanks

 

I had mine done on my e55 for cheap and I would assume it's the same process. Should be 2 to 4 bolts and it pops right out.

No need to remove the alternator. Not 100% sure this fits and just did a quick search on ebay. You can see the brushes on it and those wear down.

 

Awesome thanks. $35 from FCP Euro.

 

Not that I disagree with the voltage regulator, but I would try to connect a decent sized lead acid battery up and fire up the car and see what's going on. Check voltage etc.

I too plan to go with a protected lithium battery as well. But I'd check with a normal battery first.

 

Yeah that’s the backup plan. I still have the OEM battery here but I’m not sure my new trunk floor can handle the weight.

 

Did you bring the battery up to a full charge with a charger? I have a CTEK 7000 and it works great. Not sure if it is compatible with the battery you are using. You can leave it plugged in and it will keep your battery conditioned while the car sits for long periods. It tells you when the battery is up to full charge and has settings to recondition batteries that fall below an acceptable voltage.

As mentioned it is worth it to make sure your posts and cable ends are clean, making good contact by turning them a little on the post and ensuring they are tight.

 

Also small batteries dont have the capacity to act as the neccesary buffer of the charging system especially since there are so many electronics with these platforms.

Which could have put such a strain on the charging system and could have wiped out the regulator.

 

100% alternator issue. As mentioned, likely the voltage regulator.

 

Thanks guys. Regulator on the way.

I’ve been a little lazy and not topping the battery off with my Ctek charger, which I agree is awesome thanks Mort.

 

I also use ctek as my primary charger

 

Exact same symptoms I had a couple months ago. Alternator at idle was only charging 11.7 volts, got stranded a mile from home, car shut off.
Currently running an Odyssey PC1200 battery for the last 10 months (10k miles).
I ended up removing the entire alternator and replaced only the brushes, then retested the alternator at a local autozone, 14.3 volts tested.
Alternator brushes were completely worn.

You should be able to get to the brushes without removing the alternator, but it’s a very tight fit.
Total of 4 bolts and they’re out.

Here is the picture of my alternator out, should show you which bolts for removal.

 

AC or DC?

 

Start watching at 17:50

 

Oh. That looks like it’ll be fun to get on and off.

 

Edited, thanks for catching that, wouldn’t want anyone to be confused.

 

This is a much more complicated question than you think. In a typical german fashion the charging systems on newer mercedes aren't so simplistic. Germans don't think of a battery as only a source of power. They think of it as a shock absorber for the electronic system. When we do battery tests to determine whether they are good or not, it isn't testing it for load or max amperage output. Instead the tester is introducing a/c voltage across the battery and seeing how much comes out the other side to determine its health. I'd start by swapping to a normal battery to see if you actually have a problem. More than likely it is your newly found Lithium ion battery. There are a couple things to keep in mind. Good voltage doesn't equal good amperage . Amperage is what recharges the battery. Typical normal operating voltage is in the 13.2-13.4 voltage zone but that isn't set in stone. You should be able to view battery voltage and amperage draw/gain (sometimes displayed with an i ) in the dealership service menu area (where you go to reset the service indicator/dynomode etc...). The charging algorithms on these vehicles don't just blast the alternator constantly charging the crap out of the battery. This is can work and did work for decades but ultimately your battery would last 3-4yrs tops. It's actually bad for it. It's actually not good for the battery to be at 100%, ideally they are in the best state at 80-90% . This is attained by cycling the alternator on and off. On our cars the M.E. (ecu) provides the lin bus signal for demand output of the alternator, but that is determined by the battery sensor which sends it's data to either the front or rear sam determining the state of charge. From there via can the ecu is told what it needs to do to achieve the results it wants. They also use this for an advantage in fuel efficiency. They will typically decrease alternator output on acceleration and increase it on decel or engine braking since its basically free energy. Think of it similar to a hybrid using braking regen to charge the battery.

The mercedes lithium ion batteries all have a built in control module and specific coding to utilize it. I haven't had an opportunity to disect or compare the differences or coding changes in the other modules side by side. Obviously the newer models that came with optional li batteries will have the necessary coding changes which could be retrofitted back and forth, but I don't know that ours even have the option or coding data available.

Basically my thoughts are it's highly likely there is nothing wrong with your car it just doesn't like your battery..

 

That’s probably right. My car doesn’t like a lot of things I do to it though. Guess I’ll replace the regulator, and if it still acts up it’ll just be another thing I’ll have to live with as there’s nowhere for the OE battery to go anymore.

 

Are you referring to the EQ line?

 

It’s not the battery... I’ve been using a super tiny 3lb lithium battery for going on the 3rd year absolutely no issue other than limited reserve for leaving the vehicle between drives. I leave a trickle charger on it and a battery quick disconnect that I disconnect one of the terminals if it’s going to be away from a charging location. Like I said other than that everything else has operated the same no noticeable differences in voltage, sound quality or running a bunch of accessories

 

No refering to SLS black series, AMG gt-s, gt-c,gt-r, newer sl/s sedan/s coupe 63 and 65 cars.

Hybrid stuff is way different, with way different integrated modules. The battery has internal high amperage switching, typically a/c refridgerant running through it. You've got a dc to dc converter module for changing 12v to 48v or whatever it's running for hybrid, electric motor module, battery management module, blah blah...... Im talking about the production cars running normal size lithium ion batteries to take place of regular agm batteries. They dont both with it in lower end cheap cars since the battery is like $1700 or something silly. They weigh around 10lbs instead of 50+. They are badass but pricey. For example if you leave the key on position 2 with around a 40amp draw like an S class has the regular batteries have a slow steady voltage drop over time maybe 10 minutes in you'll be around 8-9v and everything gets angry and wont function. The lithium ions stay at full 13.2v for like 30 minutes straight and then drop to basically zero in an instant. Lithium batteries should last 10+yrs but we'll see.


On another note blkrkt. I bet if you unplug the sensor on the battery ground it'll throw a fault and default to max output on the alternator

 

Nice. TIL. I thought they all still used AGM batteries.

https://www.voltphreaks.com/technologydir.php