Hi all,

After leaving my 2016 c63S unused for 6 weeks or so whilst travelling, I have come back to a battery sign on the vehicle. This sign seemed to come and go a little, but has asked me to look at the drivers manual which unfortunately i cannot access as its in a foreign language (another story). For quite a while the car was fine, but more recently the car has stopped displaying the battery sign and is now not responding to electric key opening, rendering the car only operable via the physical key. However, the engine starts and drives fine still, with no warnings or problems in the driving or starting (via inserting the plastic key into ignition). However still, when the car is off, it again will not lock and respond to electric keys (batteries in key replaced recently). I am assuming that this is the battery but want to see if others have encountered similar behavior before I opt to replace battery. I cannot warranty the battery as im in a different country to purchase country.

Thanks for any advice!

 

While I can't comment on whether you should replace the battery, I will say that leaving any modern-day Mercedes (and most other cars) for more than a few weeks will likely "kill" the battery charge. On an older battery, this may end its useful life, especially if you experience cold-weather operation. AGM batteries can withstand more deep-discharge cycles than the older "plain" lead-acid batteries, but their life seems to be limited to about 7-8 years under ideal conditions and 4-5 years under worse conditions (i.e., more and deeper discharges).

AMGs seem to go put the (50 or so) electronic modules into various levels of "sleep"/quiescence, based upon recent usage, time and other factors. We're mostly isolating during the pandemic so have not been driving our AMGs very much ... so I've had some experience observing them. My 2016 C63 S is a very low-mileage car ... meaning that it was parked for a significant percentage of it's initial 3 years with the original owner (i.e., its battery was often deeply discharged). At the start of the pandemic, I once left it for 3 weeks and noticed that I had to use the key to start it as the keyless-go capability seemed to be put to sleep ... which, I'm guessing, is the condition you experienced. In my case, the car did a (mostly highway) trip of about 50 min. each way, shortly thereafter, and the battery/systems returned to normal behavior.

I also have a 2017-version of this battery charger (bought it because I saw the same one being used on the showroom-parked cars at my dealer)
and have since been swapping it between the 2 AMGs every day or two, in order to keep the batteries charged (in case you don't know it, AFAIK all recent Mercedes cars have a charging/battery port under the front hood ... required when using Xentry diagnostics, so the process is quite painless).

If you hook up such a battery charger and look at the battery voltage and/or percentage of charge after a few minutes, you'll get an idea of the battery's discharge state. After doing this a number of times, you'll become acquainted with the amount of discharge you get from overnight and longer parking and how long it takes to bring the battery up to a full charge. Whenever parking a car for more than 2 or 3 days, it's worthwhile attaching a battery charger/maintainer so you avoid the deeper discharges and extend the life of your battery.

 

I agree, your battery is most likely severely discharged and you haven't driven enough to fully recharge it, so some modules in the car probably remain in power saving modes. The objective of the energy management in these cars is to try to preserve enough battery charge so the engine can be started. It's doing that by progressively shutting down non-essential modules. Go for an hour+ drive or hook it up to a battery charger until it shows green for a fully charged battery and then see if the various modules are coming back to life. I highly recommend hooking up a battery tender if you are going to leave the car unused this long.

My 2019 has a standby mode in the COMAND system to turn off the telematics and Internet connection to allow parking the car for an extended period. It will even show how long I can leave it parked in standby mode before the battery needs to be charged, so I can decide if it needs to be hooked up to a tender in addition or not. I usually put mine in standby mode if I travel for at least 2 weeks and so far that's been fine. In 2019 I was gone for 2 months in Europe picking up my C63, so I hooked my previous car up to a battery tender. That's just kind of a must on modern cars. The nice thing about the 2019+ models is also that I can see the battery status in the phone app, and if the battery gets low, I get text messages and email alerts. With the much reduced driving I do these days due to the lockdowns I have noticed that my battery charge rarely says fully charged. I just had Service B done last week and I started to get battery alerts while they were performing the service. It took a few days driving it for more than an hour each day and finally the phone app reported that the battery was fully charged again.

 

thats really helpful - thanks!