C300CA

After I bought my 2011 C, I found when I start the engine, cranking speed is lower than my other two cars, but it always starts. Later I plug in a digital voltage monitor in the 12V outlet, it never reaches 12V. I tried driving a few miles and monitor it right after I turned it off, it was just 12.0V. 20 minutes later it went down to 11.60V.

I forgot what it was when I was driving. Maybe the standby current is higher due to more electronics than other cars? Maybe this battery has been on shelf too long? I don't drive it daily; it is my weekend car.

I will take the car to dealer for checkup tomorrow.

Carsy

The voltage at the battery with the engine running above idle should be about 14 volts which tells you the alternator is charging OK.

The battery should hold its charge for a week & turn the starter motor briskly .

Other makes of cars starter motors can make different cranking sound.

Interested to hear what the dealer says.

xXHotelCrazyXx

With the car running, connect a voltmeter to the battery and see what voltage it says. It should be 13-14 volts to read a proper charge, if not your alternator isnt charging properly

C300CA

Thank you both for reply.
My QX4 starts the best, taking just a very small fraction of a second. When driving, it reaches 14.3 V or so. RX300 is a bit slow but noticeably beter than my C300.

If dealer found no problem with the charging system, then I like them to put in a "new" battery. In 96 I bought a new Maxima. Battery was low so dealer replaced with a new one after a few days. Nissan can do it so can MB, I'd think.

jimmythegreek

In my 2008 C350 I had an amp and Hk system in it w no problems, was about 13-14 running even cranking the amp. My new 2011 C350 has almost the same system in it just a little more power and the lights slightly dim when cranking the bass. I checked the battery w system on and off and it never charges above 12.8-12.9 I think they are using different alternators in the new cars, Im about to go in this week and see what I can swap, either an older model alternator or higher output. I tried even revving to 3k RPMs and testing and 12.9 is most I got. So something is definitely up w the 2011s alternator/battery wise. This car has same battery as my 2008 did size/make wise

C300CA

Hello Jimmy,

Where is the battery? Is it easy to access? Thanks.

jimmythegreek

its under the hood right in front of the passenger airbag. THeres a cover over it w 3 clips you just pop and the cover comes up. Be careful putting back on, theres an air return molded into the cover and firewall must be seated well, just line up the vent, its easy if careful. You can also test right at the alternator, just make sure your meter is on good ground either way

GateKeeper

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Ausmbtech

Current MB's use the alternator differently to older models.

Most have variable output alternators to help reduce fuel consumption.

In most cases once a battery is fully charged they hold battery voltage between 12.6v-13v to reduce fuel consumption.If you apply the brakes then the voltage may increase to as much as 15v to recoup the "free" energy, if accelerating then it may drop as low as 12v. The engine ECU determines what voltage it wants to maintain at the battery based on load/temps/electrical consumers etc.

All Bluefficiency models have this, and most other current models.

They are fitted with bigger batteries to compensate for this so you will get a lower cranking voltage becasue the battery isn't aways fully charged when you park the car.

Carsy

Great info . Thank you.

C300CA

I just took a few miles drive before going to my dealer. Observation: when driving, it hit 14.8V max and 13.7V min, depending on situation like idling, braking, coasting or acceleraing. Right after I stopped and turned key to position 1, it came down to just below 12V even after auto headlight was off.

Looks like charging system is ok but battery is not good. I will show my brief data to dealer. If they refuse to replace battery, I will ask to test drive another C300 with my digital meter just to compare.

BTW, my meter is Innova from Amazon like $14 with free shipping. Forgot model number. It has three LEDs, green=ok, yellow=marginal and red=not good (my C300 is always red after engine is turned off)

C300CA

I showed dealer my data. They tested battery under the hood, not at console outlet. The printout indicates "13.19V, GOOD BATTERY". Therefore, I can't ask for a new one. Advisor told me not to worry, since I have four year warranty and any time battery fails their test they will replace it.

Before they tested it, advisor said it is not accurate to test at 12V outlet, as along the wire there are various electronics stuff drawing some current.
when I came home I tested under the hood, I got about 12.5V. I will still use my method knowing there is 0.5V difference.

Ausmbtech

With the instrument clustor showing the odometer and the ignition/key with ignition off, accessories on press and hold the "ok" and "answer phone" on the steering wheel (press the phone button slighlty before the ok button). this will bring up a service/back menu. go the vehicle data and scroll until you seen battery voltage. this will show voltage and current going to/from the battery (IMPORTANT: current is not alternator output current, this is current at the battery).

Quite interesting to see how the voltage chages under different driving situations

C300CA

Thanks Ausmbtech. Lots of info there. I see UB: 11.5V, IB: -14A but how do I interpret? I don't think the current is 14A.

C300CA

I tried driving and monitoring the voltage. When driving that info page can't be accessed. I think it's for safety.

C300CA

I need to correct myself: Before starting the engine, I bring up that info page. Then start to drive, that info is available.

I just came back from another dealer. When driving, it showed like 14 plus volt which is normal. right after engine was shut off, it became 12.0V. Technician tested with his portable meter on the battery terminals and report says normal. He also explained that MB charging system is not like most other 'traditional' system; it does not fully charge the battery for reasons (I don't remember). Howeve, based on his experience, my battery is on the lower end of normal range. He has to hold my car for half a day or so to really check where the possible leakage is.

He pointed out a white square thing right at battery negative terminal, which is a sensor to check if anything wrong with battery.

Rogwp

I had a similar experience in my 2010 C300; they had to change the battery sensor as it was causing a slow leak.

My car sat for 5 weeks once when we were away, and I had problems with multiple starts when we came back. Once the car had been on the highway the battery was charged, but the mechanic was not satisfied with the sensor and its readings. They replaced the battery and the sensor. The only problem was that the sensor had to come from Germany and I got to drive a newer car for 2 weeks!

C300CA

[quote=Rogwp;4740304]They replaced the battery and the sensor./quote]
I wonder what new battery voltage and current you can read from instrument cluster. When stopped, my raverage reading is VB: 11.5V, IB: -14A

Ausmbtech

Obviously you still have the accessories on so that you can see the battery vltage, anything above 11.4v is ok, and yes it really is drawing 14Amps. with the ignition on and engine off it wouldn't be unusual to see upto 35A current draw.

If undervoltage (enough that starting may be an issue at a later stage) then the car will start turning everything off inc the radio to protect itself against a potentially not starting.

Remember the battery is designed to sit between 60-80% charge, that's why the battery voltage is a little lower than what you would normally expect where they are normally 80-100% charged.

Rogwp

[QUOTE=C300CA;4743904]Just got my car back, I have been driving another one. I checked the readings and they were: 12.2V, and -15.8.

C300CA

Looks like 14A is normal, but to me it's huge current. With most power stuffs off, I really wonder what is drawing 14A? It doesn't look like a standby current but something high power is constantly running. I borrowed a DC current clamp meter but couldn't find an easy access to the battery cable.

Ausmbtech

It all adds up very quickly, think of each control unit drawing 200mA-500mA, there would be at least 15 that are active, throw in the amplifier for the radio, a few lights, cooling fan in the navigation and you are there pretty quickly.

Many years ago I remember working out that a W211 had a peak current draw of 35A just when you unlocked the car with the remote which dropped to 20A after about 10 seconds then held 15-20A for at least the next 2-3mins........and that was without actually getting in the car!

Carsy

The car obviously needs the battery to be in very good condition to have these loads drawn & operate the cars electrics at their optimum levels.

Ausmbtech, Is the normal wet lead acid battery sold in Australia a suitable replacement to the dry OEM MB fibreglass mat type ? ( assuming the same Cold Cranking Amps specs ). I see some do not have the correct H2 venting plumbing. There is a large difference in price.

C300CA

My C is my weekend car, maybe a couple of times during the week for very short drive like 3 miles. Do you think a trickle charger is good if I leave the charger on my C for most of the time in garage? Its price is a bit too high ($110 or so from MB).

Ausmbtech

If the vehicle was originally fitted with a glass-mat (AGM) battery then it need to be replaced with one. W211''s and W230's can get away with fitting a lead acid battery, but the battery control unit has a harder time working out the state of charge and usually shuts down battery consumers earlier than is actually required. This is solely an annoyance.

In all later type that have variable battery voltage then it is crucial to have the correct battery type fitted since a lead acid battery won't last very long when it is being charged with upto 15v. It will litterally "cook" itself and wouldn't likely last more than 12 months if it doesn't cause acid damage before then.

VHLA batteries are very long lasting if cared for correctly.
I have a small 760A version fitted to my W201 diesel that I bought new in 2003 for about $500, it's still working fine today and will probably keep going for a long time yet. When they get fully discharged then they need a bit of care to get them operational again. This is where many think the battery has died.

To recharge one you need to have a good second battery and a very good quality charger like a CTEK can detect battery condition. You need you connect the 2 batteries together with jumper leads and connect the charger. Leave it like this for about 8hrs, then dsconnect the second battery and leave the charger on for another 2days. unless they get this very full and deep charge they won't last very long before they go flat again.

I used to take alot of the "failed" batteries home from dealers and simply recharge them, only about 10% had actually failed. I have one in every one of my vehicles.