I have a 300SD Mercedes!! I can put in a brand new battery and within 1 hour the battery is dead!!?

Question

I can put a brand new battery in my 300SD Mercedes and within 1 hour that battery will be dead as a door nail!! What could be the problem? Oh!! The car doesn't even have to be running!!

Answer 1

One of the circuits in your car is drawing too much "parasitic" current, including a bad alternator as one possibility. A shop technician finds the problem by connecting a 10 Amp meter in series with one of your battery cables. It should normally read less than 1/4 Ampere (250 milliamperes), but in your case will probably read more. Then the technician tries pulling fuses one at a time until he finds the circuit or electrical connection that stops the current flow. In the mean time, you can disconnect one battery terminal to stop the excessive current flow out of the battery when the car's parked.

Answer 2

The above answer is incorrect, the rectifier bridge prevents reverse current flow, not the VR.

The first thing I'd try is to disconnect the alternator. There is a single plug on the back of it. Just pull it out (engine not running, please), and leave it out. If the battery still dies, it's not the alternator.

One possiblility is the A/C relay. You can test this idea by locating the clutch wire on the A/C compressor, and disconnecting it.

Another possibility is a vacuum leak, believe it or not. There is an electric vacuum pump located under your rear seat, which is supposed to maintain vacuum for your central door locks. If there is a leak, it will run all the time.

Finally, the one thing that could really soak up power is the glow plug circuit. There's a special 50 or 70 amp fuse for this on the firewall. If you can find it and remove it, you can test. If this is it, the problem is either the glow plug controller or the ignition switch.

Answer 3

While suggestions of an alternator problem point to a very likely source of the large current draw, what they don't explain is why the current is flowing there in the first place. I'd have a long look at the voltage regulator. It should not be allowing reverse current flow to your alternator. As those above have noted, it takes more than a dome light to kill a freshly charged battery (assuming it IS freshly charged) in an hour.

Answer 4

You say dead,That tells Me You have used a 5 Dollar to test
each Cell and they are in the Red.Called a Hrydrometer.
Man You should be seeing Fireworks under You Hood.Also
with a Short like that You would see Arc as you connected Batt.Do this at Night and look what Red Wire is Blown out.

Answer 5

Did you have the battery charged first? Usually what they do is charge a brand new battery before they give it to you; you can't just take it off the shelf and install it in your car.

good luck

Answer 6

Nothing on the other side of a fuse could kill, the battery that quick. About all that leaves is the solenoid and the alternator.

Answer 7

that is called frustration. understanding that the subsequent step is genuinely getting up, and looking out batteries, AND having to manually turn the quantity up/down, and/or the channel. that is tough. We PAY to have a distant so we don't could circulate. while that plan is going awry, we "Press" puzzling.

Answer 8

if the car has an alternator it is bad your car doesnt have to be running for the battery to be dead if your alternator is bad it will pull down a battery fast fast fast get your alternator checked.....

Answer 9

I suspect the ceiling light is on constantly. Or the glove box light. Put your car in the dark garage and check all little lights, trunk, under hood, dash....

Answer 10

If you are sure you connected the + and - terminals correctly, then your car has a short circuit somewhere.