Hey everyone, have an interesting story you all may get a chuckle out of...

I have a 2004 CLK500, it's been my daily driver for about 8 years now. Last year my battery had took a dump, so I bought an Interstate battery to replace it after having heard good things about them. Randomly last year, I noticed that my key fob had stopped working, and would only unlock/lock the car when I was standing right next to the driver door. Didn't really pay any attention to it, figured my key was going. This summer, randomly the LED's in my instrument cluster went out entirely - CEL, ABS, Brake, Turn signals all stopped working, but the speedometer/tach and clock still worked, and would light up when the headlights would be on. Shortly after, my key stopped working entirely. Ended up buying a new key from the dealer, and it would work here & there before eventually it stopped working as well. After seeking advice from 2 Mercedes mechanics whom I trust, both had pointed to my cluster problem as simply my cluster going dead. At the thought of having to spend a couple grand for a new instrument cluster, I parked the car seeing as it needs other work done to the suspension and other cosmetic things.

About a month ago I picked up a 2009 CLK550 for a great deal, and figured I'd consider selling the 04. Having sat for the last month, I planned to move it this past weekend to get ready for the upcoming winter. The battery had went dead as I hadn't started the car for over a month and the temps have been on the colder side. I didn't have my car charger at the time, so I swapped the interstate battery with a Duralast I randomly had kept charged on a tender in my basement. Once I installed the fresh battery into the car, I went to start the car and behold: all of my LED's were working again! On top of that, I noticed my key worked normally again! Talk about weird.
At this point, I'd assume the Interstate battery was giving the car some trouble. Would've been nice to know before going out and buying another CLK, even though I am in love the newer one So I guess my question to everyone is, should I attempt to contact Interstate about this issue, or just consider replacing it with an OEM Mercedes battery from the dealer and moving on. I'm aware that there is only 2-3 makers of batteries in the US. But I know these cars are sensitive to certain parts that aren't OEM. Any advice is appreciated.

 

These cars do very weird things when the battery is not quite healthy. Check the forum, lots of stories. You need a multimeter/voltmeter to check battery voltages. For a healthy battery, standard values are around:

- 14V when engine running
-high 12s right after turning off the engine (12.5 - 12.8V, or thereabouts)
- mid 12s after being stopped for 12 or more hours.

If, after a full day stopped, battery is just at, or below, 12.0v, change it.

You could also have something draining away the battery charge when the car is parked. If that's the case, disconnect the negative terminal on the battery, right after stopping the engine, wait 12 hours or more, and compare with the value above, obtained with the battery connected- A big difference will indicate abnormal battery drain.

My guess is your problems with the 04 were just a bad battery.

 

Thanks @dfrois

I will look around the forum to see what information I can gather. A multimeter is one tool I haven't invested in since I really don't dabble in electrical diagnostics. But I'll get my hands on one, recharge the battery and maybe run it over the weekend to check the values.