Hi guys,
after taking the merc in to have an exhaust system changed, two days after driving it home I opened the door, no light. Turn the key, no lights no nothing. Battery taken out, put it on charger, and the charger acted like the battery wasnt there. Next morning, put battery on charger, and says its charging. Its still charging now, 3 hours later, but Im worried whether its the battery or the alternator. I work on the car alot, its not registered so its not diven much, and I constantly charge it, this was its first major drive under my ownership and it went about 50 kilometres. Any ideas? If it was the alternator, why did the battery not recognise when on the battery charger? By the way, the battery is not the correct one, its just a temp low power till car is registered/roadworthy. Thanks in advance.
Cheers
Luke

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1971 280SE - The S Class
1974 280CE - Sterling
1988 300E - Stanley

So maybe now would be a good time to install a new battery of the correct size and cold cranking power, and then once you have the car running, you can throw a voltage meter on the battery and see if the alternator is putting out the correct voltage.

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Some of the new style battery changers will not change a completely dead battery b/c they need battery power to run the changers circuitry.
The old chargers did not have Float circuits and would have an output regardless of battery condition.
To test if you have that type charger, simply plug the charger in and touch the leads to a 12v auto lamp..if it lights , it is the old style, if it doesn't , it is the newer.
It is alway good to have an old changer hanging around just to get a completeky dead battery back up enough so you can use the newer circuitry chargers [ which, discounting this fault, are much better].
You can also ususally get a dead battery to accept enough of a charge for the new chargers by jumping it from another battery for a few min.............

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A Dalton

well do this get a multimeter and set at 20V DC current and conect it to the battry with the car running you should get about 12.56 or 13.01 if it charges good the current on the battry should be higher that what it was before started if the current is the same then the alternator is not working does the red light come on sometimes while driving this means the brushers are worn out we'll try to find out whats wrong

Check the engine to body ground strap. It runs from the right rear of the block (usually a starter mounting bolt) to an 8 mm bolt connected to the frame rail area. It runs across the exhaust pipe header. Quite common to have a well meaning exhaust guy pop the copper braid while they are doing an install.

Don't have a clue regarding the battery charger situation. Dead batteries quite frequently won't accept a charge at first.

I wasn't aware of the "float circuit" but it certainly explains the no charger read problem.