NOTACAR

Two keys came with automobile (CPO purchase) '09 CLS 550. One key is fine. Second key always shows change (replace) battery on display..have changed battery twice (dealer replaced twice once at time of purchase). Use key on Saturday, display shows again replace battery. Any ideas will be appreciated. FYI..car is under original warranty. Dealer states, " we don't know what's causng the problem. Sated they reset something (don't know what they reset but it didn't solve the problem). I certaintly intend to push the issue, but need ammo to deal with dealer. I am thinking replacement of the key. What do you guy and/or gals think? Thanks in advance for any help/advice.

konigstiger

If first key has been fine all along and second key repeatedly malfunctions speak with Service Manager to approve replacement key under warranty. In the meantime, check for and remove any soil or grease from battery or battery contacts using lint free cloth and alcohol.

NOTACAR

Thanks Kon...will do. I was hoping I would get a response from you. I haven't been a member of this forum long, but I have always valued your response to other member's problems. You are definitely one of the best on here. I will post the outcome after dealing with service manager.

rwm21cls500c

I had a similar problem with my only smart key.... and I was very worried that something serious was up...... I'm a computer/network tech and decided to open it up again and check the connection prongs that these type of keys have. I carefully bent the connecting prongs so that they would make better contact with the battery... already had replaced these expensive batteries twice.... and put it back together.

No problems with it since..... and that's about a month. Can't be sure that will help you, but who knows. Careful of your warranty, don't want to break the prongs.

NOTACAR

Thanks RWM. Because I still have warranty, I think I better let the dealer figure it out instead of taking a chance with voiding the warranty. I like tinkering with automobiles, but only when it is absolutely necessary. In this case, it is not necessary. The dealer will have to solve this issue. I am beginning to think the key issue was a problem during the CPO processing/inspection and/or they didn't check the key when the vehicle was returned off lease. Nevertheless, I really appreciate your response and advice. I will post the results. Thanks again.

Saks_C350_Sport

Sorry to bump an old post guys. I'm having similar issues with my 09 CLS550. My normal key has been showing replace batteries frequently. I replaced them both with no change. Two nights ago I was driving and the dash turned red and showed no communication with the key. When I bought the car in July, the MB dealer ordered and provided me with a brand new second key. I tried that one yesterday and am getting the replace batteries message with that one as well. Anyone have this happen to them before? Thanks in advance.