Battery weirdness... - PeachParts Mercedes-Benz Forum

bhatt · #1 01-19-2008, 09:00 AM

I have a 2 year old Interstate battery in my W140 500SEL. Never had a problem with it, but have heard these cars go through batteries quickly. It is now on it's 3rd Canadian winter.

I usually park the car in the garage, but was visiting relatives in Detroit a few weeks ago. Parked the car on the driveway and didn't drive it for 24 hours (it was 0 degrees fahrenheit, so pretty cold out!). I then started it to move it off the driveway (car ran for maybe 15-20 seconds) and shut it off. Didn't drive it for another 24 hours.

I went to start it and it would turn over but not quickly enough to catch. I cranked it for a few minutes (so there was obviously juice in the battery, just not "enough" to turn the starter fast enough). Hooked up jumper cables, waited 20 seconds, and it fired right up.

Haven't had a problem since (although it's been garaged every night since).

Recently, when I start the car after a really cold night, it throws an ASR light and goes into limp home mode. If I immediately shut it off and restart it, there is no problem for the rest of the day (even after making multiple trips)

My theory...
Battery is dying. Reserve capacity is fine, but the cranking amps are significantly reduced. Car starts with low levels of battery juice, so it throws an ASR error code. 2nd try starting the car works find (there is obviously no ASR problem) because there is enough voltage to keep the system running fine.

Do I need a new battery? Or could this be another problem like an alternator? I am assuming with the cold weather/parking outside issue, it's likely the battery but don't want to change it if not necessary.....

Help!

Thanks..

manny · #2 01-19-2008, 10:09 AM

I would start by taking some actual voltage readings.
Voltage at rest, voltage during cranking, voltage after start-up.
No offense, but I've never been a fan of Interstate batteries.

platt-deutsch · #3 01-19-2008, 10:28 AM

I just had the same issue with a interstate batt in my S600.
I made a adapter to fit the lighter socket and hooked my digital voltmeter up.
charging voltage was 14Volts. With engine off the voltage would drop at once to 12.1 Volt.. If I ran the heater on REST for about 8 min. the low battery symbol would apear on the heater readout. The voltage would drop to 11.55 volts.. I went to Interstate dealer and they put a fancy electronic tester on it and said the Battery is OK... but the voltage is about 1 volt low..They of course told me it just needed charging..BS
I argued long enuf and they did give me a new battery as it was only 8 months old.
All the problems went away.. Voltage now stays above 12.3 Volts with heater REST mode on for up to 25 min.

manny · #4 01-19-2008, 10:33 AM

I could write a book on Interstate horror stories.

Like the time they got sued for placing 1000 cca stickers on top of 800 cca stickers & selling the batteries as 1000 cca.

cdplayer · #5 01-19-2008, 11:28 AM

I do not live in an area that is as cold as some of you. But I too had a battery issue with my S500. My mechanic asked me, after all the goodies had been reprogramed back into the computor, if I lock the car while it is parked in my garage. It is not a daily driver as my 500SEC is.
The question seemed kind of odd, but he said if the car is at rest and not locked, the systems within remain "awake". In other words, there is a greater draw on the battery when the car is off and unlocked. Locking the car when not in use will keep the battery performing at it's best. Taking into account you have a good alternator too.

platt-deutsch · #6 01-19-2008, 05:38 PM

I really doubt if that is true if you dont lock the doors.. I doubt if it makes any difference..

bhatt · #7 01-20-2008, 02:59 PM

Went out to the car this morning and it was 47 degrees fahrenheit in the garage. Car had been left overnight in the garage.

Voltage before starting the car: 12.17v

Voltage while cranking: 8.5v (it started up right away but that's the lowest voltage I saw)

Voltage once running AT IDLE: 13.0v (only measured it from engine start until 20 seconds later. Assuming it didn't go higher than that later on. Did not rev engine above idle at all.)

Any thoughts? I know the voltage when running seems a bit low (shouldn't it be 14v?) but the alternator is old.. it doesn't need to be replaced yet though does it?

My conclusion is that the battery sucks.. 12.17v sounds really low to me for a battery that "should" be fully charged. Car was driven 30 minutes last night before I put it in the garage, so it should have been "fully charged" when I put the car away for the night. The cranking voltage sounds really really low to me too!

Should I start by getting a new battery under warranty or do I have an alternator issue? Or something else?

Thanks!

junqueyardjim · #8 01-20-2008, 03:29 PM

At the first sign of low electrical power availability, I would dump the battery. Typically, it is a number one problem, and if you have two or three years on a battery and you live in a area where 4 or 5 months you have cold weather, it is by far the easiest, lowest cost repair you can make. Yes, yes, you could suck out a number of months of additional use, but is it worth it.

Xsbank · #9 01-20-2008, 04:09 PM

If you only get 13 volts and you drive short trips your battery will never charge properly and you will have to replace it more often. Depending upon temperature, a battery charger will put up to 'about' 14.5 volts initially and will taper off as it charges. It should only take a few minutes to recharge as you are only pulling a few amps out of the battery.

CCA makes it harder to figure out, but for an example, if your battery is rated as a 800 CCA battery, the standard requires it to put out 800 amps for 30 seconds at 0 degrees f and to not drop below 10.5 volts.

Your battery requires a proper session with a battery charger, or it may be toast!

A fully-charged battery should be 12.6 volts after it has sat for a while (24 hours, if I remember correctly) and 13.8 right after charging.

Your alternator/regulator is probably not working properly.

John T · #10 01-21-2008, 12:59 PM

Hi Bhatt I have read with interest your post as I suffered a simalar problem
with my 1995 S420.Doing short trips and in my case not using the car every
day the battery failed to turn over the engine a few times.Maybe your
alternator requires checking but the solution in my case was to purchase
a CTECK intelligent battery charger which I leave hooked up all the time
the car is in the garage.With all the various items sitting across the battery in
the off position, sometimes unless trips are longer with lights off (daytime)
the battery may never reach full charge.

Regards John Thttp://www.ctek.com/EN-US/DealerLocator.aspx

Chester UK

PS Charger Model No CTEK XS 3600

Zeus · #11 01-21-2008, 01:37 PM

Neal -

Battery at rest should read about 12.7V. With engine on and idling, normal load, it should read about 13.75V or so. Try increasing the load (lights, heater) and check V at idle and also at 1500 RPM or so. See what the values are. If they stay high (at or around 13.5V) you know your alternator is working.

Also check the alternator brushes to see if they are worn and may require replacment. Your 13.0V at idle reading seems very low.

C.

Zeus · #12 01-21-2008, 01:43 PM

Here are some readings I made when I replaced the alternator in my 300E. The original stock 70A alternator was failing and I upgraded to a new 80A unit. The original 70A still worked, but only barely. Under load, it couldn't produce enough juice to keep things going and charge the battery.

BEFORE (70A):
rest - 12.85V
idle - 13.86V
idle with full load = 11.87V
full load, 1500 RPM = 11.74V

AFTER (80A):
rest = 12.88V
idle = 13.97V
idle with full load = 13.56V
full load, 1500 RPM = 13.94V