Checking the state of the battery

[MBManInKen]

After hearing about John's current battery problems, I was thinking that perhaps I should check up on the state of my battery now that we've entered the shorter days season.

For clarity, nothing is wrong (touching wood ) as far as I know, but better safe than sorry.

Now, in the good old days, I would disconnect the battery so that there would be no draw whatsoever and would expect to see a voltage of about 12.5-12.7V. I would then reconnect, start the car and check for about 14V or thereabouts over its terminals indicating that the alternator is working properly.

I can obviously do the second test easily, but what about the first one? If I disconnect the battery, will I have all kinds of grief resetting windows, roofs, steering wheels, etc?

Any other test I should do? As it's one of those modern maintenance-free batteries, an acid test is not really an option.

 

[television]

After hearing about John's current battery problems, I was thinking that perhaps I should check up on the state of my battery now that we've entered the shorter days season.

For clarity, nothing is wrong (touching wood ) as far as I know, but better safe than sorry.

Now, in the good old days, I would disconnect the battery so that there would be no draw whatsoever and would expect to see a voltage of about 12.5-12.7V. I would then reconnect, start the car and check for about 14V or thereabouts over its terminals indicating that the alternator is working properly.

I can obviously do the second test easily, but what about the first one? If I disconnect the battery, will I have all kinds of grief resetting windows, roofs, steering wheels, etc?

Any other test I should do? As it's one of those modern maintenance-free batteries, an acid test is not really an option.

By modern ones, do you mean AGM battery

 

[BlackC55]

Many garages have digital battery testers and these are probably the best way to test one.

Midtronics is the company that makes the best testers.

MB dealers use them to decide weather a battery under warranty is good or bad.

 

[MBManInKen]

By modern ones, do you mean AGM battery

It's dry alright, but don't know if it's AGM technology, I would need to check and I'm in the office - the car is at home.

 

[television]

It's dry alright, but don't know if it's AGM technology, I would need to check and I'm in the office - the car is at home.

All 211's have a AGM battery I think, on these you cant use a normal charger it must be a fixed rate at 10% of the battery capacity

 

[fredfloggle]

After hearing about John's current battery problems, I was thinking that perhaps I should check up on the state of my battery now that we've entered the shorter days season.

For clarity, nothing is wrong (touching wood ) as far as I know, but better safe than sorry.

Now, in the good old days, I would disconnect the battery so that there would be no draw whatsoever and would expect to see a voltage of about 12.5-12.7V. I would then reconnect, start the car and check for about 14V or thereabouts over its terminals indicating that the alternator is working properly.

I can obviously do the second test easily, but what about the first one? If I disconnect the battery, will I have all kinds of grief resetting windows, roofs, steering wheels, etc?

Any other test I should do? As it's one of those modern maintenance-free batteries, an acid test is not really an option.

The standard system draw would cause such a small amount of voltage drop that it is not worth considering - you can leave the battery connected and make the test - easiest way is enter the engineering menu (assuming available on your car) and monitor the battery voltage with no load , and also with lights on - suggest you do this on a cold morning before the first start . With modern quick starting cars it is much more difficult to see battery condition deteriorate - until of course it won't crank .

 

[fredfloggle]

All 211's have a AGM battery I think, on these you cant use a normal charger it must be a fixed rate at 10% of the battery capacity

AGM's like constant current charging until 14.7 volts is reached , then the voltage should be locked while the current is allowed to drop .

 

[grober]

this is a good article http://www.landiss.com/battery.htm as is this http://www.batteryfaq.org/ I have always found from bitter experience over the years that in the winter months with low ambient temperatures if you have any battery problems its a sure indicator its failing to hold charge ( unless there's a "one-off "specific identifiable problem) If its more than 3-4 years old then its probably on its way out and should be changed. On modern cars its such a VITAL component that its replacement should be incorporated into the manufacturers recommended service operations (bit like the key fobs) :bannana: It would save a phenomenal amount of money and anguish for owners and MB dealer recovery services. That's my mercedes "employee of the month "suggestion.

 

[television]

All cars should be like the SL with 2 batteries, one does nothing but start it

 

[Diesel Benz]

...make the test - easiest way is enter the engineering menu (assuming available on your car)...

Considering the engineering menu, I did find the guide on the voltage readout for the W221 but I was not able to make the car accept my request. Anybody else with a W221 who has been successful?

Don't have the order of buttons at hand, can post it if anybody would be interested trying.

 

[MBManInKen]

Thanks everyone for your comments. I'll test over the weekend and if i'm unsure, I might play it safe and get another battery.

 

[glojo]

Thanks everyone for your comments. I'll test over the weekend and if i'm unsure, I might play it safe and get another battery.

Any reputable garage should test the battery for you.

Regards
John

 

[television]

Any reputable garage should test the battery for you.

Regards
John

If Halfords are supposed to be reputable they are not, their testers show bad batteries to be good and good batteries bad to increase sales with no come back

 

[television]

If you have a voltmeter, then test before you start the car, if the car has been used in the last few days then it should be near 11.75v min, though the car will start OK. the best way to test is after the car has been used and then stood for a few hours, if the voltage is under 12v then you have a partial short circuit cell

 

[MBManInKen]

Malcolm, thanks, that was what I was going to do - with my analogue multimeter .

When I'll test it will have stood for 5 or 6 days.

I just don't have any data on what its draw is when not in use, and I didn't want to disconnect the battery out of fear of having to reinitialise/reset loads of stuff .

 

[television]

Malcolm, thanks, that was what I was going to do - with my analogue multimeter .

When I'll test it will have stood for 5 or 6 days.

I just don't have any data on what its draw is when not in use, and I didn't want to disconnect the battery out of fear of having to reinitialise/reset loads of stuff .

Do it after some use on the week end, its impossible to measure any battery unless it is charged, and do after a few hours from then.

No need to disconnect