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NigelP

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I have a 2008 Mercedes c200 which is dead in the driveway. It starts perfect and quick when jumped but does immediately after being switched off (doesn't turn back on unless jumped). I tested the voltage with a multimeter and got the following

Stress no accessories 1.5rpm 13.77
Stress with accessories 2.5 rpm 13.67
No stress idle 13.76

Battery off 10. 13

I am inclined to assume battery, but I have noticed lately that 6 bulbs have blown which may be alternator. What's does everyone think?
 
Battery is dead.
pop in a new one an you will be good to go.
 
Are you expecting it to start after it has been turned off after just a jump start with little or no charge , or have I misunderstood your post.
 
Are you expecting it to start after it has been turned off after just a jump start with little or no charge , or have I misunderstood your post.
I have jumpstarted it, driven for 30 minutes and it runs fine, I turn it off and it won't start again after 5 seconds.
 
Is it completely dead or does it crank, 30mins driving is not a lot depending on your engine size, especially if you have AC on . Does it crank when you try to restart it, and have you tried to charge it with a conventional charger?
 
Is it completely dead or does it crank, 30mins driving is not a lot depending on your engine size, especially if you have AC on . Does it crank when you try to restart it, and have you tried to charge it with a conventional charger?
The starter motor attempts to turn once then the power is gone, the computer then blacks out and the lights all turn off if I twist the key again then about 3 or 4 minutes the battery is showing 8-9 v again, directly after turning the car off without turning it back on the battery dips to 12.2 V but won't start form that, it attempted to turn the start which chugged for a bit then the voltage drops to about 8 and it stops. Once jumper leads are put on it jumps with ease. The first trip I took was probaly closer to an hour with ac blaring and daytime running lights on and the second 30 minutes. No issues at all especially when driving.
 
Your battery will not charge great from flat in the conditions you describe , and it would use a good percentage of the charge to run the accessories unless it has a second battery fitted , some Merc's do.
Give it a good conventional charge, depending on the charger and amp hours of the batteries this could take up to 48 hours.
What is the size of your engine?
 
Your battery will not charge great from flat in the conditions you describe , and it would use a good percentage of the charge to run the accessories unless it has a second battery fitted , some Merc's do.
Give it a good conventional charge, depending on the charger and amp hours of the batteries this could take up to 48 hours.
What is the size of your engine?
It is a 1.8L supercharged. I don't have a battery charger and am stuck with the issue being that a new battery will probaly not he far off buying a new charger. I honestly am not to fussed about buying the battery but I am more wary I could buy it and it could end up being the alternator. I always assumed if the alternator was operating over 13.5 V then it should be fine, but given the symptoms lately of fast blowing light bulbs, I am only thinking of it as a possibility.
 
An alternator is designed to replace that charge lost during starting and it can take a while for it to do this. If the battery is flat or has a low voltage the alternator will never charge it no matter how far you drive.

Modern cars have very specific power requirements and need a stable voltage to run correctly. Charge the battery or fit a new one. Most vehicles charge at around 14.5 volts.
 
Are you certain you did not leave anything on that would have flattened the battery to a level it would not crank?
 
An alternator is designed to replace that charge lost during starting and it can take a while for it to do this. If the battery is flat or has a low voltage the alternator will never charge it no matter how far you drive.

Modern cars have very specific power requirements and need a stable voltage to run correctly. Charge the battery or fit a new one. Most vehicles charge at around 14.5 volts.
So the alternator should be performing at a volt more then it is.
 
Take it do a well equipped garage that has the equipment required to test the battery properly , they will also test the alternator for you. They will know if the battery is defunct if they have the proper gear to test it with. The equipment is quite sophisticated now.
It is worth the extra to have it done properly.
 
So the alternator should be performing at a volt more then it is.
The battery could be pulling the alternator voltage down. An alternator needs voltage to operate correctly so a dead battery will not help.
 
As above, replace the battery and get the alternator checked to be on the safe side.

And don't buy a cheap brand battery. They are a waste of money.
 

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