W220 dead battery

[grober]

Sounds like a faulty alternator diode or voltage regulator to me. Take it to an auto electrician / Bosch service centre for testing. You should be able to purchase a professionally reconditioned unit [ with warranty]for about half the price of a new one.

 

[design guru]

Is there a guide or diagram to removing the water-cooled alternators as some people have mentioned it is fused to the engine block, will it come straight out or do I need to remove any major components to clear room for it to be extracted?

Any thoughts on replacement brands, I have seen a Lucas alternator from ECP which comes in at £160 new once the old unit is returned or some reconditioned Delphi or Bosh units for £100. Anyone used a Lucas version or do owners prefer to replace the unit with the same brand thats in there currently?

 

[Ted]

There is no way that your battery is draining by 1 volt every ten seconds unless it is seriously faulty or there is a high resistance to the point you are measuring.
13.85 volts isn’t good but is still enough to give the battery a decent amount of charge - you may find that the battery is so flat/faulty that even full output isn’t allowing the voltage to come up further.
Couple of things to do - check with an ammeter to see if there is a permanent discharge. Start on the highest scale first.
Check the charging current when it is showing the 13.85 volts. May be easiest/best to do this with a clamp type ammeter. Not the most accurate, but the safest method.
Really, given the above, it might be best to get a good auto electrician to take a look.

 

[design guru]

There is no way that your battery is draining by 1 volt every ten seconds unless it is seriously faulty or there is a high resistance to the point you are measuring.
13.85 volts isn’t good but is still enough to give the battery a decent amount of charge - you may find that the battery is so flat/faulty that even full output isn’t allowing the voltage to come up further.
Couple of things to do - check with an ammeter to see if there is a permanent discharge. Start on the highest scale first.
Check the charging current when it is showing the 13.85 volts. May be easiest/best to do this with a clamp type ammeter. Not the most accurate, but the safest method.
Really, given the above, it might be best to get a good auto electrician to take a look.

This is the second new battery I connected and when connected its fine, as soon as I start the car it runs fine but still only showing 13.85v and no battery light appears in the dash and according to my MBii Scanner it remains at 13.85-13.90v whilst idling, no increase when revved, as soon as the car is off the scanner shows 12.5v which is what it should be for a fully battery and keeping an eye on it began to drop within 30 second it dropped to 10v and was still showing a decent in voltage so I disconnected the battery before it went completely flat. The first battery I put in I didn't check the voltage as I just thought my old battery was the problem and within 30 minutes of going back to the car it was at 0.5v. I only left it for 30 minutes as I was washing my dads car.

 

[Ted]

First of all, not doubting for a second what you say
I’ve had a good think.
Assuming your battery is good.
It’s going flat in around 1/2 hour - my guess is that a 100Ah battery at the 20 hour rate would probably give around 100 amps for that period of time before becoming flat. That’s around 1200 watts continuously. Something WILL be getting very hot.
It’s unlikely to be any of the ‘normal’ consumers as they will be protected by fuses and current limiting devices.
You’ve eliminated the obvious - the block heater, so all that remains are the starter/solenoid - but I’m sure there would be additional symptoms here or the alternator (a diode failure could cause this but you can usually sniff them out). The low charge voltage would also suggest this as there would only be two of the phases providing DC current (I bet if you were to put a scope across the battery there would be a shed load of ripple if a diode (or two) was short circuit.
Just as a fyi, a shorted rectifier diode in an alternator is often accompanied by a very noticeable whistle, changing with engine revs.
Definitely worth disconnecting the main alternator feed before buying a new one to see if this is the root cause (don’t start the engine with this off)
As I say. At around 1200 watts, something, including the supply wiring will be getting very warm.

 

[grober]

Does your alternator look like this?
2001 S600 Water Cooled Alternator Replacement

e.g.
https://www.benzworld.org/attachments/install-alternator-01-s600-pdf.1362434/

 

[design guru]

First of all, not doubting for a second what you say
I’ve had a good think.
Assuming your battery is good.
It’s going flat in around 1/2 hour - my guess is that a 100Ah battery at the 20 hour rate would probably give around 100 amps for that period of time before becoming flat. That’s around 1200 watts continuously. Something WILL be getting very hot.
It’s unlikely to be any of the ‘normal’ consumers as they will be protected by fuses and current limiting devices.
You’ve eliminated the obvious - the block heater, so all that remains are the starter/solenoid - but I’m sure there would be additional symptoms here or the alternator (a diode failure could cause this but you can usually sniff them out). The low charge voltage would also suggest this as there would only be two of the phases providing DC current (I bet if you were to put a scope across the battery there would be a shed load of ripple if a diode (or two) was short circuit.
Just as a fyi, a shorted rectifier diode in an alternator is often accompanied by a very noticeable whistle, changing with engine revs.
Definitely worth disconnecting the main alternator feed before buying a new one to see if this is the root cause (don’t start the engine with this off)
As I say. At around 1200 watts, something, including the supply wiring will be getting very warm.

Strangely enough I have had a high pitched whistle coming out for a few month which I never diagnosed as it would sometimes disappear. Had the AA and myself look at it and the sound was coming from behind the engine closer to the firewall and gearbox area.

will definitely remove the alternator and get it checked, looking at the price for a new diode and voltage regulator will probably set me back £60 and a recon alternator is £100 so I will probably take the recon route as the car has covered 240k. Thanks for the advise so far.

 

[design guru]

Does your alternator look like this?
2001 S600 Water Cooled Alternator Replacement

e.g.
https://www.benzworld.org/attachments/install-alternator-01-s600-pdf.1362434/

Thanks, I will get under the car and check, thanks for the link. It’s bloody cold at the moment. I have a plan to get the car in the garage where it will be easier.