I'm at a complete loss. I noticed a rougher/slow start about a month ago, but it would go away sometimes. Knew it was a definitive issue when I went away for the weekend to come back and find the car wouldn't start at all. I have read everything online along with talking to my local shop about fixing this, but they don't have the capacity to dig into a potential battery drain issue. Battery and alternator tested fine. I purchased a new battery

Not sure what is causing battery drain/rough start. The battery was replaced December 17, 2015 with an "AutoCraft Platinum AGM Batter, Group Size H6, 760 CCA." I have used a multimeter to establish that I have a 12.4ish resting voltage reading which makes sense due to the way these are made to "save" mpg. That is after car is asleep. Battery reads 14.2ish when started. (Readings taken yesterday morning after having taken out fuse #2 overnight, but I still had a rough start). I have tried to determine the parasitic draw. I disconnected negative cable and found that I had a draw of 0.09 amps which seemed okay. But then again, it usually starts in the morning just extremely slow and sometimes feels like it won't turn over then it does. After leaving it for the weekend it won't even begin to act as it will. I removed each fuse to determine what the cause may be. Fuse #2 controlling such things as the seat adjustment, keyless go (I don't have), etc. brought the reading down to 0-0.02 amps. I still thought it would have been okay since 0.09 isn't high but expected something around 0.05. Not sure of a short or anything somewhere or if the BCM would need to be updated (not sure if I can determine if that has been done?), but I would think this would have been determined in removing fuses. It doesn't seem to be related to the evaporator fan coil (noticed it for the first time running an hour after I started car). I don't hear it running once car is asleep nor did removing fuse #22 (assuming that's the fuse that controls it) do anything to the draw when asleep. I was not able to remove all fuses in the engine compartment due to not being able to reach them, but based on pulling #2 fuse as described above you would think I wouldn't have the issue. I also removed all fuses on the SAM control module which did nothing.

Did more testing last night and this morning. Here is the timeline:

-3.5 hours after getting home at around 9pm battery at 12.49 volts. Started slowly and battery was at 14.1. Readings seems normal/average.

-45 minutes later at 9:45, 12.47 voltage reading on battery. 14.15 when started, slow start again.

-1 hour later at 10:45, come out to find that evaporator fan is running (assuming it is right behind battery pretty much above/behind glove box. Tried pulling fuse #22 to stop it. Did nothing. Tried opening my door which did nothing. Even opened the trunk and it stopped. Tried clicking the close mechanism which did show it as closed and it didn't start back up, but it did when I actually closed the trunk. Opened again and closed and it stopped. But this is the first time I've noticed this having taken the cover off of my battery I get out of the car the past week. Never seen it on. Car cranked fine now. Turned off and got out to find the reading at 10.5. Turned it off and waited a bit to a slow start again. Turned off and checked to find 10.1. Assume it is still pulling a decent amount having just been turned off.

-6am this morning. 12.42 volts before I cranked. Went to start and clicking as if it was dead. Waited about 15 seconds (checked voltage and read 9.65) then tried again to a slow/rough turn to actually starting. Battery ran at 14.15 after starting. Charged the battery on "battery tender" while getting ready for work and it showed 12.65 with a slight slow/rough start. Had voltage reading on engineer menu on way to work. Supply voltage (HU) showed 14.3V and Battery voltage via CAN showed 14.2V.

-Did this the previous night and had gotten 12.1 volts and 13.7 A while sitting in the car. Volts jumped to 14.1 when turned over and was accelerating in park. IB read 27.5ish A and accelerated then stopped and did it again and eventually dropped to 24.5ish.

Would you all have recommendations, have experience with a similar issue, or be able to determine something that I can't? I refuse to go to the dealership with anything, and I would love to get this sorted out ASAP.

 

+1 or there's something in your starter circuit that's shorted. The voltage readings you're getting aren't consistent with slow turnover....they are fine. 12.45V = 75% SOC. The 14+V after start means you are charging OK. There's another thread about the "smart charging" MB uses now that keeps it around a 50% SOC (12.24V). "-6am this morning. 12.42 volts before I cranked. Went to start and clicking as if it was dead" It should have turned over fine.

 

Curious to see what voltage reading you get after letting the car run a bit. Mine would read 14.3V at first but then drop to 12.6V after a little while and stay there. I guess that's the smart charge saving me gas and shortening the life of my battery.

The evap fan running after is a known battery killer. Others have posted that after bringing their car in for drained battery that the dealer changed setting so the fan would not run later to dry evap. Might be worth looking at in your case.

 

I don't know if 350s had this issue but my 2010 E550 needed a firmware update to charge the battery correctly. As far as I know only an official MB dealership can do this.

 

So, I recorded some more readings last night...

I have found no fuse box under the steering wheel when I take the cover off, but I did try determining the battery drain again last night. I disconnected the ground clamp, and it always starts around 5 amps and creeps downward for the next minute or so. It was consistently bouncing around between .06ish to .12ish and as high as .22ish. Would never stay on one consistently even with pulling all of fuses in the engine compartment and SAM module one at a time. I will note that this was done more than an hour after I had last had the car awake. Battery was at 12.4ish volts before I did this. I did hear a clicking ever so often as if the computer is consistently monitoring the pull on the battery. It's as if a switch is being flipped. Meter would jump a tad every time it clicked. It was a sequence of like a few minutes before I would hear it then "click." About 30-60 more seconds pass then "click" back off? Has happened any time I am under the hood. It happens regardless of it I am checking battery with the multimeter.

Anyone know about checking the SAM's quiscent current? Is that the fuse pullng?

I left the battery tender on it all night to find that it starts up just fine. Is it possible that it is such a small pull that can depend on the circumstance? Potentially a shorted circuit or sensor of some sort going bad? This is about to drive me crazy as I've seen with most battery drains.

I was quoted by another local shop that deals with mainly foreign cars that claimed they had a "special" computer that allows them to determine which modules are "awake." The place I generally take my car was not able to handle such a task with their capacity, and I figured I would try something other than the dealership here.

In terms of checking the readings on my car when driving, consistently stays at the 14.3 and 14.2 range. Haven't had it drop like that while driving.

Thanks!

 

Just thinking this through.....if you had a battery, battery drain, or charging problem you wouldn't be seeing the SOC that you have. I've had no problem starting with a 12.1V SOC. If it struggles at 12.4V but starts fine at 12.6V that leads me to believe it's in the starting circuit because the difference in SOC of 75% to 100% shouldn't be noticeable to the starter. Check the wires to the starter to see if one is shorting against the frame/motor/bracket etc.

 

That definitely seems like something I was thinking it could be.

I know that the starter is difficult to access. Could you give me a little detail on how to determine if this is the case? Is it possible to determine/access from looking down on the engine?

Thanks!

 

I'm guessing you need to remove the under panels and access it from underneath and I don't know how much of it you can see. My only advice is do it when everything is cooled down. My first check point would be the hot wire going to the starter.....it should be the BIG one and check it end to end for possible shorts to ground.

 

I know you said you got a new battery a month ago, but it may be worth taking it out and to the store to have them load test it while not connected to the car. They will likely charge it up first, but you've got to see how the amps hold up under load. Voltage can be misleading - I had a bad battery that was showing adequate volts but didn't have the amps in reserve.

 

Definitely follow Fisch's advise and load test the battery. Just went through this parasitic drain issue with my wife's van. Load tested the battery and all good. It turned out to be a stuck rear tailgate latch mechanism. If the van sat for more than 1 day it would need to be jumped. These parasitic drain issues can be a real pain to locate and fix. Good luck!

 

Parasitic drain is not the issue if SOC stays within starting range. He's getting a good SOC but a bad start symptom. Yes, he could have a bad battery but the one it replaced had the same symptoms. Coincidence? Unlikely but possible. Never take anything for granted when troubleshooting. I ended up putting a slow charge port outside the vehicle so I could access battery SOC without opening the door/hood and waiting for the battery voltage to stabilize. I wasn't having any issues it was just preventive maintenance that started me with the w212 battery. Now I trickle charge it once a week or so. Poor system design that allows a minuscule saving at one point to override reliability and long term maintenance costs. My wife's BMW uses similar charging algorithms.

 

To be honest, I try to research and get into doing what I can, but I must say that I don't have any knowledge with this and would probably screw that up. Any other suggestions? A different way to pinpoint that?

 

I've considered doing this as well, but I feel as if it will be able to handle the load test unless I leave it for a day or so then go try it out. I guess it's worth a shot before I start spending more time and money to have someone else fix it.

 

Well, I left the tender on the battery last night. Car was around 12.6 before anything. Drops to 12.3 when my roommate got in car and put key in ignition. Seemed right to me. Then cranked and got only as low as 11.1. Seems like this would be okay. Just doesn't make sense. When I don't leave the battery on the tender at night it starts at around 12.4. Haven't been able to get him to be able to do the cranking while I read the meter yet without the tender being left on it overnight. That is what I plan to do tomorrow morning. Still seems odd. But with a fully charged battery, I never have an issue with the what could be the starter. Is that normal? Does that signify electrical issues or a short of some kind?

I greatly appreciate all of the feedback I'm getting. I don't know a ton about cars, but I'm trying to learn.

 

https://www.google.com/url?sa=i&rct=...69885713613622

12.3v is 70% charge, 11.1 is dead.

 

Based on what I have been reading, 12.6ish is 100%, 12.4 = 75% and 12.2 = 50%. There should be a drop when cranking due to the pull on the battery to get the starter to fire. I just don't know how much of a drop is okay. I have read different things such as a drop resulting in the voltage dropping no lower than 9.5 is okay assuming it goes back up upon actually starting which is what happened with my car. I have also seen that a drop of .6 or .7 is what you would expect with these cars along with my local shop telling me that a drop below 12 is not good. I'd say I'm a little confused. If that is the case, would seem it has something to do with my starter, but to what extent, I have no clue.

Like I said, I'm open to anything.

 

alternator or a starter.

 

I'm not a professional mechanic but I've always worked on my own cars and done a lot of work with electric bugs....including Mercedes (not that they are unique in that respect). With the w212 I've found: the "smart charge" may save gas (very little IMHO) but it leaves the battery in a constant low SOC. With 'low' being about 50%. .04V is lost overnight if the car has been driven that day and the AC drying cycle kicks in. .02V - .03V is lost if it's not used at all. The battery SOC must be checked in the quiescent state. Opening trunk or doors wakes up the system and you need to wait about 15 minutes for it to get back to normal (same with other later MB). I've had the car start with no problem at a 12.1V SOC but it should start at 12.0V as 11.9 SOC is technically 'dead'. Someone suggested having your "new" battery checked.....do it. The odds are low it's bad but you don't know for sure until it is given a load test. Your symptom is also consistent with a battery having a good SOC but not starting the car because it breaks down under load. SOC is good for a battery and charging system quick health check but it doesn't tell you if the required cranking amps are there.

If you don't feel comfortable poking around the engine bay above and below and looking for shorts...like wires rubbing insulation off or hot parts melting it....then have an indy do it.

 

Thank you for the suggestion. I plan to have the battery load tested just because it won't cost me anything, and then I'll have the wires and all looked at. It's worth a shot before having someone run diagnostics on everything. Any experience with having the ECU settings update so that the alternator operates as a normally functioning system? I've read some things on that. Of course, this is if nothing is found in terms of the starter.

 

do you experience longer crank when you start the car?

 

I've heard of the AC drying cycle being turned off but my experience shows that to be a minor drain and not worth deleting. I haven't heard of anyone changing the "smart charge" algorithm.

 

Well, I spent let it sit over night on Friday due to getting a 10.4ish voltage reading before I went to bed. Seemed weird being that I had yet to get anything that low. Anyways, woke up to same thing Saturday morning. Made no sense considering I could crank and would eventually turn over after sounding as if it never would. Very frustrating and confusing to me.

I finally decided to get an extension for my socket wrench and take the battery out and to Advance Auto Parts. It was actually diagnosed as a bad cell in the battery. Got a replacement and has worked fine ever since. I guess what throws me off about all of this is the fact that it would start but with very painful sounding noises that would get it going. It never wouldn't not start except for the weekend I was gone for two days and didn't use the car at all. Is this a sign of a potential problem that may cause this battery to go out? Could anything besides an alternator cause the battery to eventually develop a bad cell? It was just so odd considering what I had read of the reliability of the battery I had purchased.

 

thefisch called it!

 

One bad cell is all it takes to render a battery useless. Always start with the easiest diagnosis and that's why we all said to load test it. I doubt you will have any more issues. Happy motoring!

 

I guess what threw me off was how I was getting 12.4 voltage until Friday night, but the problem had been persisting for roughly a month. Is it possible something else is causing an issue or can a battery actually be bad without showing it?