jspbtown

So I give my son a 2005 CLK320 cabriolet for a graduation present. It has 40k miles on it. I have had it since Jan in my shop going though every aspect of it to make sure it was as reliable as possible.


He is home for 2 weeks and drives it every day and it worked flawlessly.


He starts his new job and on day 3 he comes out to start it and its dead. The fob worked. The dash lit up. But no crank. It does not turn over...nothing.


So please reassure me that he left a interior light on. He said he checked the headlight switch and it was off (it was raining yesterday when he left work so he probably used his headlights).


What are the odds it is something else? And what might that be? I read about fuse #52 being under "amped" so could it be that? Anything else?


Like I said...maybe he just killed the battery by leaving an interior lamp on or the headlights and he just doesn't want to admit it.. He is about 2 hours away so I can't really did into it.


Possibilities?

Yidney

You might search the forum for things like "battery dies overnight' or whatever variations on that theme occur to you. I suggest that only because I know there have been a number of such threads about parasitic drains on the battery, I just don't recall the cures. But first things first. Has it started yet with either a jump or new battery? You don't say. Obviously if it still will not start, you have a different issue. Also, I assume that year also has a built in voltage meter. Have him access it and tell you what it says. Have him turn off everything - AC/lights/radio, etc. Then tell him to scroll the center screen until it is at the outside temp screen. Then have him remove the key and reinsert it and turn it just one click, then tell him to press the odometer reset stalk on left side of the cluster three times. He should then be looking at a voltage reading of the battery.

jspbtown

OK...we were able to check the voltage through the display. It was 10.4 volts and that was after he tried starting after work and it turned over a bit. Clearly not enough to start the car.

So he got jumped and it fired right up. He is off to have the system tested and if everything checks out he will get a new battery.

I also told him to make 100% sure that ALL the interior lights are off.

Yidney

I should also have mentioned that once he has the voltage meter displayed, he can start the car and drive it with it on so you can see what is happening. If it goes up to 14 volts while driving, then that pretty much tests the alternator for you.

jspbtown

OK...making progress.

Autozone checked the battery and charging system and said they were in good working order. I had my son activate the internal voltage gauge and it was reading between 14 & 14.2 volts while driving. When he had the AC and lights on it would drop to 13.9 volts.

I am thinking the little stinker might have left something on last night.

I guess we will see tomorrow.

Yidney

If it starts tomorrow, after the battery recovers a for a couple days he should do two things. (1) Check the voltage first thing in the morning before he starts it or does anything else, and (2) watch the voltage as he starts it. The voltage change on startup will be hard to see because it starts so fast, but look to see if it drops into the 9s. If the cold morning voltage is below mid-12s, or the start voltage drops below 10, get a new battery anyway. I just bought a replacement for my original 2008 battery today. It's been marginal for a while. 12.1 stone cold and about 9.6 on start.

Yidney

Just for a frame of reference, I installed my new battery this morning. A Bosch AGM. It read 12.7 volts before doing anything, but only dropped to about 11.4 while cranking at startup. Almost two volts higher than my old battery.

jspbtown

So my son texts me this morning. It had 12.3 volts when he went out and it started right up. He drives it to work and it is in the 14.4-14.5 volts range the whole drive to work. Works until 5:00 and goes out and its dead again...back to 10.4 volts.

Any ideas? He is off to see if he can get the battery changed. Not entirely hopeful given its location. I think he is going to have to Uber to work tomorrow...get another jump...and then come home Friday for a new battery.

I will check the battery for drains based on the sites I have seen.

Rudeney

Yes, first check for drains. If nothing is apparent, then replace the battery. Autozone's quick tests are not always accurate. To get a proper test, the usually keep it overnight on a charge/discharge cycle. If the battery is more than 5 years old, I would go ahead and replace it.

jspbtown

So some additional info/ Please remember the car is about 100 miles away right now and I am doing most of this data gathering over the phone.

So after the car is dead at my son's work he gets it jump started. Starts right up and he goes about his business and drives it for about an hour. When he gets back home he calls and we start going through some things.

The car I shut off and I ask him what the volts say. He says "12.1". I tell him to start it and watch what the volts drops to (like Rudeney suggested). He turns the key and nothing. Its a no start. I ask him what the volts are now and he says "10.4".

Now I am thinking battery. When driving it is putting out 14v (+/- .5). He drives for an hour and then tries to restart it and its a no go. Now my repair days are looooong gone by but this reminds me of a dead "cell" we used to see back in the day.

Thoughts?

Yidney

Seems like it almost has to be the battery. If it was some unrelated fault, it does not seem like the voltage would suddenly drop in the battery. Did you notice if it was an MB battery when you were looking the car over? It might be 12 years old.

jspbtown

I am relatively sure it is not an OEM battery. I had hooked up a trickle charger to it when I bought in in January because it was going to be in my shop for 4 months and I think it was black with yellow writing on it but I can't recall the brand.


So I am looking at an AGM battery and I think I have narrowed it down to two.


Battery 1: From Pep Boys. It is a Bosch. Cold Cranking Amps:850...Cranking Amps:1020...Amp Hour:90...Reserve Capacity:160


Battery 2: A Duralast Platinum from AutoZone. Cold cranking amps: 900.....Cranking amps:1000......Reserve Capacity: 160


The Bosch has a 4 year warranty while the Duralast has a 3 year warranty. Both are essentially the same price.


So....more CCA or longer warranty??

Yidney

I got the Bosch at Pep Boys because if I stood in the store and ordered it online for in-store pick up it was only $179, about $11 cheaper than the one Rodney recommended, plus it was about 8 pounds lighter. But it don't think it matters. 850 is plenty of amps.

jspbtown

So I purchased and installed a new Bosch AGM battery this evening.

I did the test with my multimeter and had some interesting things happen but I think I understand why.

So the new battery was 12.7v before install. I installed the battery and hooked up the positive terminal (after a thorough cleaning of all contact points). I place one probe on the negative terminal of the battery and then the other lead on the disconnected negative cable. There is a small spark and the reading is about 1.85. So I think "great....I have a draw". So as I look at the meter it drops down to .25 in about 15 seconds.

I do this several times and each time the same thing happens. Make contact with the terminal, the reading is right around 1.85 and then it drops to .25.

I then open the door and the interior light comes on and the center of the speedo lights up. I check the meter and it reads something like 3.25. I watch that for a few moments and it pretty quickly drops down to .25.

So here is my logic...when I hook up the multimeter I "wake" things up and they cycle through and then drop back down to where I think they should be.

Is that reasonable>

Rudeney

Yes, that is a reasonable assumption. BTW, I'd use an inductive ammeter instead of an inline tester. Harbor Freight has clamp-on multi-tester one for under $20.