Car Battery Health and Replacement

[ericycle]

Hi,

My question is this: do these cars usually have warning signs and symptoms that the battery is nearing its last days?

The car in question specifically is a 2006 C200 CDI. The battery is a little over 4 years old. A few weeks ago, I've had about 2 instances when I got a low voltage warning on the dash before starting. And about twice the cranking took a bit longer than normally. This was a few weeks ago. Since then no warning or slow cranking.

Today I tested it directly with a multimeter. I turned the headlights on for about 2 minutes, then turned them off. The reading was 12.4 / 12.5 v. When starting the car several times, the voltage would drop to about 9.2-9.8 v.

Although interestingly, afterwards, I monitored the voltage from the secret menu in the dash, and when starting, it wouldn't go lower than 10 v. Maybe thought just because the engine was warmer...

One more piece of information that may or may not be relevant: about half a year ago, we were on vacation and the car was not started or driven at all for about 2.5 weeks, and despite a low voltage warning, it started just fine.

 

[190]

Measuring the no load voltage is an indication of the state of charge of the battery and 12.5 volts is only a touch low. Rather than use the headlights immediately after running or charging to remove the surface charge I prefer to fully charge the battery then leave it overnight to make sure the car has gone to sleep and only then take a reading. Assuming it's a normal wet cell battery 12.6 volts or above would indicate full charge.

Measuring the voltage while cranking is a form of load test and 9.8 volts would be considered quite good. Your battery doesn't sound too bad at all from those readings but the only real way to be sure is to have it properly load tested.

 

[ericycle]

I actually had it tested at a local auto store. The problem is getting a decent explanation from the employees there and interpreting the results.

I'm guessing he did a load test (i'm not yet quite clear on all this). He said that my battery was at 250 amps or something, and that for a battery rated at 730 amps, it was bad. I asked, they said anything under 50% of the rated amps is bad. Obviously, I'm 250 is considerable less than 50%, so that's a stupid criterion, since I might have been at 50% 2 years ago, and still had no problems for at least 2 more years.

I googled this a lot and couldn't really find anything - how do I know how many amps at minimum are necessary for me to be able to start the car? The ambient weather is generally over 10 degrees Celsius.

 

[rf065]

He said that my battery was at 250 amps or something, and that for a battery rated at 730 amps, it was bad. I asked, they said anything under 50% of the rated amps is bad. Obviously, I'm 250 is considerable less than 50%, so that's a stupid criterion, since I might have been at 50% 2 years ago, and still had no problems for at least 2 more years.

My battery was tested and found to be 45%, if the car was left for 4 or 5 days, the battery only had power to start it first time or went flat. However one morning after sitting out only one night at -5 degrees the battery was as flat as a pancake. How does yours compare?

Russ

 

[ericycle]

My battery was tested and found to be 45%, if the car was left for 4 or 5 days, the battery only had power to start it first time or went flat. However one morning after sitting out only one night at -5 degrees the battery was as flat as a pancake. How does yours compare?

Russ

According to this excellent article, there are 2 distinct parameters to look at. The CCA and the battery capacity. It sounds like your CCA was decent, at 45%, but the capacity was very low. Although, I don't know the effects of -5. That could be a big factor, since I don't ever start the car at anything below 5 degrees, and usually more than 15 degrees.

I'm getting the impression that while my cranking amps are pretty low, at about 35%, I can start the car multiple times with no problem, so my capacity is still OK?

 

[markjay]

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Apologies for the thread hijack....... does anyone here work for a battery manufacturer or otherwise professionally involved with the manufacture or servicing of Lead-Acid batteries? I need some general advise regarding the case of a Lead-Acid battery (not automotive) that was the cause of significant damage. The issue is subject to an insurance claim so I am not at liberty to provide full details just yet.... will anyone who can and are willing to help make themselves known please.... thanks.
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[190]

I actually had it tested at a local auto store. The problem is getting a decent explanation from the employees there and interpreting the results.

I'm guessing he did a load test (i'm not yet quite clear on all this). He said that my battery was at 250 amps or something, and that for a battery rated at 730 amps, it was bad. I asked, they said anything under 50% of the rated amps is bad. Obviously, I'm 250 is considerable less than 50%, so that's a stupid criterion, since I might have been at 50% 2 years ago, and still had no problems for at least 2 more years.

I googled this a lot and couldn't really find anything - how do I know how many amps at minimum are necessary for me to be able to start the car? The ambient weather is generally over 10 degrees Celsius.

The 730 Amps mentioned will be the Cold Cranking Amps (CCA) rating of the battery. CCA is defined as how many amps the battery will deliver at -18 Deg C for 30 Sec without the voltage dropping below 9 volts. Obviously it isn't convenient for the load test to carried out at -18 Deg so the the tester estimates it by measuring the batteries internal resistance. The result is not very accurate.

The question about how many amps the starter draws is hard to pin down. A starter motor may be rated at say 600 Amps but most or the time it will draw very much less than that. 250 A for example is enough to start a car engine most of the time. The simplest measure is the load test you did yourself. If the voltage while cranking stays above 9 volts then the battery is still serviceable. Whether you would still measure at least 9 volts while cranking under very cold conditions is another thing. If a car is habitually garaged you can take more liberties with an old battery than if it sits outside all night. I had a car battery last 12 years in my old 190e but it went very suddenly in the end so I was taking a big risk.

If it was me I would start by making sure the battery really is fully charged using a battery charger. Then I'd monitor the rested voltage to check it remains fully charged in use. If the warning message doesn't come up again this winter it should at least see you through the summer.

 

[Minden99]

I find easiest way to properly check batteries is find a good autoparts shop or garage who have a midtronics battery tester. It takes just a few minutes either on or off the car to give you battery health check. Tells you full condition of battery from goosed (tech term) , discharged but just needs recharging etc etc. It's an ace peace of kit we use in truck industry at dealers to.

 

[ericycle]

I've been monitoring the voltage almost every time I start the car. I'm getting the feeling that while I have postponed the purchase for 2 months, the end is nearing.

Yesterday when starting the car after not being driven for about 2-3 days, the initial voltage was only 12.1 - 12.2, and I actually got a 'low voltage' warning. It still cranks just fine, but I fear the capacity is pretty depleted.

Now I am wondering about the replacement battery. Currently what I have has 730 CCA and a capacity of 90 Ah.

I want to get a Varta battery, and on their site and everywhere, what comes up for my C200 CDI is E11, which is 680 CCA and 74 Ah.

I just wanted to know, if this is also compatible, than what is the actual bottom line difference for me that I might feel after switching to a battery with lower capacity and cranking amps?

It's also significantly cheaper, so I am very inclined to buy it.

 

[markjay]

I've been monitoring the voltage almost every time I start the car. I'm getting the feeling that while I have postponed the purchase for 2 months, the end is nearing.

Yesterday when starting the car after not being driven for about 2-3 days, the initial voltage was only 12.1 - 12.2, and I actually got a 'low voltage' warning. It still cranks just fine, but I fear the capacity is pretty depleted.

Now I am wondering about the replacement battery. Currently what I have has 730 CCA and a capacity of 90 Ah.

I want to get a Varta battery, and on their site and everywhere, what comes up for my C200 CDI is E11, which is 680 CCA and 74 Ah.

I just wanted to know, if this is also compatible, than what is the actual bottom line difference for me that I might feel after switching to a battery with lower capacity and cranking amps?

It's also significantly cheaper, so I am very inclined to buy it.

Is the current battery original MB, and is this the battery that came factory-fitted with the car?

If so, then I would keep to the same spec, because online catalogues can be inaccurate.

If it is not an original battery, then someone (previous owner) may have fitted a higher capacity battery.

But have you checked prices for original MB battery? They are very reasonably priced from what I gather (and usually made by Varta anyway).

 

[rf065]

I just wanted to know, if this is also compatible, than what is the actual bottom line difference for me that I might feel after switching to a battery with lower capacity and cranking amps?

It's also significantly cheaper, so I am very inclined to buy it.

Do both batteries have the same physical dimensions?
There are two battery options for my CLK, different sized batteries and the mounting clamp is different for each too. Mercedes wanted around £25 just for the clamp if you need to replace it, worth bearing in mind.

Best place for batteries is https://www.tayna.co.uk/ if you have not already tried them. I went for a VARTA AGM battery rather than the cheapest.

Russ

 

[ericycle]

It's a 2006 W203 C200 CDI with over half a million KM. I'm sure it has been through many batteries.

How can I find out what the original battery spec is, or even just a minimal or acceptable spec for this car?

Although the E11 Varta comes up pretty consistently in many catalogs and shops everywhere. But regardless, if I am offered something else when I am about to buy, how do I know if it really does fit this car?

With regards to an original MB battery. Nothing is reasonably priced here (Israel), especially original MB parts. On average, each part costs about twice as much here than what it does in Europe, and original MB parts even more and usually much more.

 

[ericycle]

Do both batteries have the same physical dimensions?

There is actually quite a difference in their dimensions. The Varta is significantly smaller than what's in there now. I was wondering about that as well.

 

[markjay]

This is what the Bosch catalogue says for your car:

30 AMG/ 200/ 220/ 270/ 320 CDI [203]

05.00-07.07

95Ah 850A(EN) - Model S6 002 - P/N 0 092 S60 020

100Ah 830A(EN) - Model S5 013 - P/N 0 092 S50 130

74Ah 680A(EN) - Model S4 008 - P/N 0 092 S40 080

I would go for the S5 013:

And the dimensions are:

 

[markjay]

The Varta version of the Bosch S5 013 is Varta Silver Dynamic 600 402 083

 

[ericycle]

I'm just trying to understand, what would I actually lose, in a real bottom line way that I would feel, by downgrading to a 74Ah 680A battery?

How would I ever really feel this difference?

Especially if I don't need to start the car in particularly cold weather, nor need to run a stereo with the engine off, etc. Why pay more for higher capacity and more cranking amps?

I'd be very grateful to anyone who can clarify that.

 

[rf065]

If you stay in Israel, very hot weather can have the same effect as very cold weather on a battery, so I would stick with the bigger battery for your car.

I experienced odd electrical gremlins like you get in cold UK winter time but I was in the South of France where it was almost 40C at the time.

Russ

 

[ivan1983]

The smaller capacity battery may not last quite as long as a larger capacity battery as it will be using more of its "capacity" each time you start.

Unless you do lots of short journeys I think you will be fine, or maybe if your glow plugs start to go bad the larger battery will be able to crank for longer before giving up.

Personally I would go with the larger capacity as I like to have "spare capacity"

 

[leef44]

that's useful to show the dimensions.
I went to Costco to get a new battery for my Suzuki. They have a big book with pretty much every car model in it. I got suspicious when the recommended battery looked too small (it's a fixed clamp, non-adjustable on my car so it has to be the right dimensions).
So I went back to the car, measured the battery then got a completely different battery in the end.

 

[190]

I'm not clear what we are comparing the 74AH 680A battery against but while your proposed battery is in good condition you'd lose nothing in terms on starting. 680 CCA (cold cranking amps) should start the car fine as the starter motor is not capable of drawing that much current.

My own opinion is MB oversize the batteries for a couple of reasons: 1. to cope with the ongoing current draw while they go to sleep and 2. because they are making the engine management systems so much more sensitive to voltage that they feel there always need to be something in reserve. Modern cars don't tolerate a failing battery like they used to. That might mean one disadvantage would be the length of time the car could be left without a charge for example parking at the airport for a couple of weeks .

Ultimately a bigger battery will have more reserves when it's on it's last legs but a smaller capacity battery should still work fine for a number of years. It worked for me because I've down sized a battery before knowing I wasn't going to need a full 10 years out of it. It still lasted well enough and was fine when I sold the car after 5 years. Conversely I've also oversized a battery in the past and made it last 12 years.

I will consider downsizing again when mine is due but while I'll be happy to sacrifice a little in terms of Ah capacity from 85Ah down to 74 Ah, I'll look for the best CCA I can get in the 74Ah battery size.

For a car application a very minor advantage of a smaller battery is that it will weigh several KG less. Weight reduction through battery selection is becoming more of a thing with motorcycles where Lithium batteries weighing just a 1 or 2 KG are starting full sized motorcycle engines. They would start a car engine too but with very little in reserve in terms of capacity.