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Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3723
Experience:  15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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I have a 2003 500SL it has been to a Mercedes dealer The

Customer Question

I have a 2003 500SL it has been to a Mercedes dealer The Electric consumers offline comes up they replaced 2 batteries an the altenator and still not fixed now they also said they did a hard reset to the computer to no avail
Submitted: 1 month ago.
Category: Mercedes
Expert:  Lou P. master tech replied 1 month ago.

Hello, my name is***** and i will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

Expert:  Lou P. master tech replied 1 month ago.

couple of questions for you

  1. how many miles are on the car.
  2. how often do you drive it
  3. did they say anything about the battery control module
Customer: replied 1 month ago.

36,000 miles they saying it needs a new command unit Very little use 2 3 thousand miles a year

Expert:  Lou P. master tech replied 1 month ago.

ok, so , when you are not driving the car do you use a battery charger on the car? on either battery?

Customer: replied 1 month ago.

NO I have put a trickle charger on before I replaced batteries and alternator but see no reason to have to

Expert:  Lou P. master tech replied 1 month ago.

ok, so when the car sits like yours does you at least need a charger on the rear main battery, the cars do not like to sit for more than a week with no starting and charging, if you are seeing the message on the dash that is because the main battery is draining when the car is not running. if it happens over night or 1-2 days then there is an excessive draw, if it only happens because the car sits for a few days or more then its normal to see that message. that is a function of the car. to avoid this you need to install a charger on the rear battery. the front battery is only used for starting the car. so there is no need for a charger on this one.

Customer: replied 1 month ago.

This makes no sense to me this is a $100,000.00 auto I think there has to be another issue

Expert:  Lou P. master tech replied 1 month ago.

well, i would like a little faith here.

Expert:  Lou P. master tech replied 1 month ago.

it doesnt matter how much the car costs, a battery will not last that long with it sitting . i am telling you this from 16 years experience.

Expert:  Lou P. master tech replied 1 month ago.

you came here for help, i am giving you help that you need. there is a reason i asked the questions i asked about the car. cause it matters

Expert:  Lou P. master tech replied 1 month ago.

the reason mercedes put 2 batteries in this model was because most customer store them, so when you go to start it the starter battery under the hood is what starts the car, then a module switches over to the rear main battery for the functions of the car and if the voltage is too low then the consumer offline message comes on the screen until the battery is fully charged, so in one sense its a normal operation in another sense it can be avoided if you add a charger to the main battery. this is not the first time i have dealt with this. i cannot force you to believe me so let me know your thoughts, i hate to think you would disregard my info .

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