Bought a new battery from Costco this past February. Installed it without issue and used my Foxwell 530 to reset the alternator. I'm the second owner of the vehicle and was not aware of the fact that the vehicle never really sleeps and is continually drawing current unless you lock the vehicle which is kind of crazy since I park it in my garage.

What are you guys doing to prevent electrical draw on the battery while it's parked?

TIA for any tips

 

First level is to keep key 30 or 40 feet away from the car, or place key in Faraday bag, and that also reduces the risk of theft. If you want more reduction in the cars electrical usage, turn off theft alarm functions. I hook up a trickle charger every few days to keep the battery topped off.

 

If parked in a safe garage, turn on standby mode.

 

With a new battery, you should be fine for at least 2 weeks of idle time unless you've added some accessory or there's a malfunction. Longer than 2 weeks, I use a maintainer.

 

As the OPs have already indicated, use a trickle charger if the car is not driven for more than 2 weeks. I use two trickle chargers (Motopower MP00205A, 12 V, 800 mA Automatic Battery Charger, Maintainer, Trickle Charger and Desulfator, $16.99 on Amazon) to keep the batteries in our two M-B cars at about 30 % SOC when we travel (I thought they would charge to ~100 %, but it's not the case.)

The alarm, the collision sensors and communications functions (remote access, over the air updates etc.) slowly drain the battery; one day I'm going to use a multimeter plugged in series in the 12 V battery circuit to measure the drain current when the car is locked.

 

30% SOC seems low -- a maintainer should be be keeping your battery much higher than that. If your battery is recently new, I'd buy a different charger. If you're measuring SOC at the jump terminals using a hadheld battery analyzer, check the battery diectly at its terminals.

 

I agree; I was surprised myself.

To resolve this mystery, I'll use my Fluke multimeter inserted in series into the battery circuit and measure both the trickly charger and the drain current values--and post it here when ready.

 

I own a C63. Largely similar electrical architecture, except your GLC has MBUX and my C63 has COMAND 5.5. It is true that there's always a battery draw, but it's largely due to the online services that maintain a cellular connection and are always ready to respond to requests from the Mercedes me app. As mentioned above, Standby mode can be activated to turn off all consumers if the car is parked for an extended period. This will also tell you how long you can leave it that way. I get over 20 weeks if the battery is fully charged before turning on Standby mode. Keep in mind, it also turns off the alarm, as the alarm still drains the battery when the car is locked otherwise, so standby mode turns it all off to maximize the standby time.

I drive only about 4k miles per year, mostly weekends and sometimes it sits for several weeks. During the lockdowns I periodically put it on a trickle charger and I replaced the battery last year, but otherwise I don't do anything special. The new battery definitely holds the charge longer, though. My older trickle charger started to indicate that the battery was bad, which is what made me replace it. I only drove it 2 or three times over the last four weeks or so. I was away in Japan for two weeks and got back Sunday a week ago. Drove it once shortly after coming back, but it's been sitting unlocked in the garage since then and I just checked the battery in the Mercedes me app and it still shows it as fully charged. I had the car in standby mode while I was in Japan.

In my experience, locking the car or leaving it unlocked makes no difference. As said, if you lock it, then the armed alarm system uses battery. The key fobs themselves go to sleep after 2 minutes if they don't sense any motion, so there's no need for a faraday cage or keeping them far away from the car. Never been an issue for me.

 

Thanks to everyone's suggestions.

I drive her 2 to 3 times a week and hook the battery charger/maintainer the other days of the week when she's idle.

As everyone alluded to the tech in the car can seemingly overwhelm the battery. I do like the simplicity of my ML550 but the GLC63 is light years ahead on multiple levels.

 

On my 2020, I did an actual test of putting an ammeter inline to give me the true reading for the battery usage when idle. Even with the doors unlocked and the key fob near, the current draw settled extremely low after the car went to sleep in about 5 minuites.

So the parasitic draw is definitely not the issue with my car. The big issue is that these cars have much more complex charging systems to save a few pennies on gasoline. The system limits the current to the battery to the bare minimum to reduce the load on the engine from the alternator. If something is wrong with the system, the battery is not fully charged even though it is getting 14+ volts from the alternator.

So that's why you think there is a parasitic draw draining the battery, but in reality, your car is likely not charging the battery fully while driving to keep it topped off and you will get low battery warnings.

 

You didn't say what the sleep mode current was, but I'm guessing it was in the vicinity of 50 milliamperes (which sounds really small). But if you do the math, it adds up quickly. Assuming that (a) your battery's capacity is 100 Amp-Hrs (typical for an H8 size), (b) that battery management system doesn't charge more than 80%, and (c) that you don't want the battery's charge to drop to less than 50%, this 30% difference (80% - 50%) is 30 Amp-Hrs. At 50 milliamperes discharge, this comes to 1.2 Amp-Hrs per day, and the 30 Amp-Hrs are consumed in 25 days (about 3-1/2 weeks). And as a battery ages, it becomes less efficient and can develop internal leakage that causes self-discharge, giving the appearance of a parasitic load somewhere in the car's electrical system.

 

Sorry to say, you guessed wrong. I wasn't joking when I said it was extremely low. You guys are all chasing the wrong problem.

 

Did you notice any wake-up intervals when the current increased? I can't make out the connections where the ammeter is connected. You removed the battery's red cable from the + terminal, and placed the meter's red lead on the battery's + terminal and the meter's black lead on the red cable?

 

Let me stop you right there, bro. I am an Electrical Engineer from a top engineering school in the US. I know how to measure current draw, so don't even try it.

 

The electrical engineers that work for me write reports which do not require me to ask questions.