Battery Drain

[Splitpin2]

Help please, following extensive testing and monitoring into why my A Class W169 battery goes flat in after three days unused in the garage, I have three questions. (I am confident that drain current is well below 50ma but battery still collapses after three days.)

1) The alternator performs well it produces 14.1 volts even with a full load of Air Con etc and i monitor it with a DVM during journeys.
I have noticed that it does not produce a charge Voltage until I put the car in gear. (Not revs related, revs dont produce the 14V just putting it into gear does) and so it could be a few seconds before it is charging, it runs fine no problems and leaves the battery at !2.6V after any journey.

2) Externally charge the flat battery (new one from MB) after 24 hours it reads 12.29V before being refitted is that an excessive drop? in the greatest scheme of things? It will start the car and there will be no problem while the car is in use.

3) As a matter of interest only I have noticed that with the battery removed there is a constant 300 mv seen across the open battery leads,
where could that be generated?
Thanks for looking

 

[Spinal]

If you disconnect the battery - whats the drop over 24-48 hours?

 

[grober]

12.29 Volts after a full recharge is not right should be in the nature of 6x2.2volts=13.2 volts Suggests there is something wrong with your charger or the battery--- perhaps the plates are sulphated with it sitting in a state of discharge for a period of time. Depending on age and history you may have got a duff one from MB you need to get it tested.---- If the alternator is charging OK the simplest solution 9 times out of 10 is a new battery. Some Intelligent chargers can sometimes be used to revive sulphated batteries but usually require to be set in a special high current battery reconditioning mode.

 

[Ted]

Help please, following extensive testing and monitoring into why my A Class W169 battery goes flat in after three days unused in the garage, I have three questions. (I am confident that drain current is well below 50ma but battery still collapses after three days.)

If the drain current is below 50ma then a good battery will not drain in three days, therefore that is your problem. Either the drain current goes higher than 50 ma or the battery is faulty

1) The alternator performs well it produces 14.1 volts even with a full load of Air Con etc and i monitor it with a DVM during journeys.
I have noticed that it does not produce a charge Voltage until I put the car in gear. (Not revs related, revs dont produce the 14V just putting it into gear does) and so it could be a few seconds before it is charging, it runs fine no problems and leaves the battery at !2.6V after any journey.

Interesting that it does not charge at idle, but I suspect not a problem - my KIA stops charging when going uphill, and starts again going downhill/on the level, so it may be an 'eco' thing

2) Externally charge the flat battery (new one from MB) after 24 hours it reads 12.29V before being refitted is that an excessive drop? in the greatest scheme of things? It will start the car and there will be no problem while the car is in use.

That is low. either your charger is faulty, or the battery hasn't been on for long enough. I would expect a good 1.5 V higher than that even for a faulty battery. It could also be that you are using an inaccurate DMM

3) As a matter of interest only I have noticed that with the battery removed there is a constant 300 mv seen across the open battery leads,
where could that be generated?

I think that that is a red herring. DMMs have a very high input impedence and will show a voltage from the smallest current source of which there may be many in your car (from electronics with capacitors as an example) I think that you can safely ignore that.
Thanks for looking

My bet is either a dodgy battery - easily checked, but it must be fully charged, or the drain is greater than 50ma (or becomes greater than 50 ma)

 

[Tim01]

Help please, following extensive testing and monitoring into why my A Class W169 battery goes flat in after three days unused in the garage, I have three questions. (I am confident that drain current is well below 50ma but battery still collapses after three days.)

1) The alternator performs well it produces 14.1 volts even with a full load of Air Con etc and i monitor it with a DVM during journeys.
I have noticed that it does not produce a charge Voltage until I put the car in gear. (Not revs related, revs dont produce the 14V just putting it into gear does) and so it could be a few seconds before it is charging, it runs fine no problems and leaves the battery at !2.6V after any journey.

2) Externally charge the flat battery (new one from MB) after 24 hours it reads 12.29V before being refitted is that an excessive drop? in the greatest scheme of things? It will start the car and there will be no problem while the car is in use.

3) As a matter of interest only I have noticed that with the battery removed there is a constant 300 mv seen across the open battery leads,
where could that be generated?
Thanks for looking

Hi
I have the same problem with my wife's w169
She also has a juddering gear box, not sure if they are related ?
Did you manage to sort out your battery drain problem?
Tim

 

[tonyc280]

I agree with Ted, a possible faulty battery.

 

[A1EK]

I had an issue with my battery despite givign good Volts did not seem to hold the power for long. I had bought a car voltmeter display that I connected inside the car permantely and noticed that when I sat in the car with the engine off after about 5- 10 mins I got a beep alarm from the voltmeter when it dropped below 12V indicating to start the car to charge etc.
The battery I had was old and was in the car when I bought it. I solved my problem with just buying a new battery. I looked on line and found a really heavy duty one for my CLK 230K that stated high 'Cold-cranking amps' which is an indictationon the 'strength' of the battery. Now the battery will last for hours with the radio on and lights without starting the car. I can leave side lights on all night and the car still starts !

The company I used was great and called The Car Battery Experts | The Battery Guys - The Battery Guys

Im not sure on your engine size but for an A Class Petrol 1.4 1998 - 2001 They do a heavy duty 500 Amp Cold cranking battery for £59 with normal battery at £44.

I would think about buying a new battery (heavy duty) . Forget the dealer !!

 

[Splitpin2]

And how many batteries would you buy.
I have two batteries both New from MB showroom, both are exactly as specified from the A150.
Both charge externally correctly and left disconnected both will sit for weeks at over 12.6 V or more at which point either one will start the car.
Both charge correctly in car where I have a DVM connected across the battery via a switch
Starting load V drop is very slight and all current checks are as per MB service sheet. Alternator runs at 14.2V come hell or high water and if the battery is removed after a run it will be OK three weeks later.
The drain measured with a digital ammeter in series and with a clamp on ammeter drops to less then 50ma a few minutes after the car is turned off.
No reason whatever to buy yet another battery or anything else at present, pointless changing alternators and such without any indication at all of a problem.
The car does not fail in use only after a few days sitting in the garage.
I even bought a Maplins in line fuse checker and monitored all fuses for the heck of it one at a time. Also disconnected external things like the towbar.

 

[Aza]

Splitpin2, did you ever fix this??

Aza
A150

 

[kenny1000]

I had this problem with my E Class, battery going flat after 3 days even though the alternator was fine and a new battery was fitted also MB literally accusing me of making it up, turned out to be the back SAM unit.