The_Judge

I'm driving so little in the age of COVID that my brand new battery is running down. Today I was barely able to get the car started, and once it turned over i got a series of strange messages on the display, such as this:

STOP CAR
LEAVE ENGINE RUNNING

RIGHT SEATBELT INOPERATIVE
SERVICE REQUIRED

SOS NOT CONNECTED

Thinking of getting a trickle charger, but I have a few concerns:

1. Are they safe?
2. Do they harm the battery if it's left connected for several days?
3. Is there one that you can connect and disconnect without having to pop the hood?
4. Any other thoughts or recommendations?

Thanks!

ua549

Battery maintainers are safe and can be left connected over extended periods of time (months).
As far as connecting via 12v outlet in the car, i.e., cigar lighter, NO, generally those are disconnected when the car is turned off.
I've used a Battery Tender Plus for several years without any problems.

The_Judge

Thanks, but I need a little education — it plugs into the cigarette lighter? That's it?

The G Man

I use the battery tender as well, just need to make sure the unit will charge AGM batteries. Theres a quick disconnect in the cables but you will need to open your hood. Charging thru a cigarette port might require the ignition to be on.

kingscorpian27

I had a similar experience working from home for the past 2 years. I purchased the The Everstart MAXX BC50BE 15 Amp Smart Battery Charger and Maintainer delivers serious charging power in a compact and lightweight package. Controlled by an advanced microprocessor, this bench battery charger automatically detects your battery's voltage and then applies the needed charging amps to ensure superior performance and long-lasting battery life. This means you can leave this charger connected to a healthy battery all winter long, and when you come back your car, truck, RV or jet ski will be ready to go. There's a 50 Amp Engine Start mode designed to help get you back on the road fast, and a Battery Reconditioning mode that can help optimize performance even with older batteries. A built in Alternator Check can even help diagnose some difficult automotive issues. Let me add that I used it to restore a dead lawn tractor battery and used it all summer without any further issues.

The Everstart MAXX BC50BE has all the practical features of professional-grade shop equipment without the professional-grade price. It's also ETL certified and backed by a manufacturer warranty.

50 amp bench battery charger maintains and charges any AGM, GEL, or WET automotive or marine 12V battery
• Fully automatic high-frequency charging delivers 3 stage charging, automatically switching from fast charge, to top-off, to trickle charge
• Battery reconditioning feature helps extend battery life; 50 amp engine start helps start your vehicle in about 90 seconds
• Equipped with reverse polarity protection for safely connecting clamps to battery terminals
• LCD screen displays charging status and battery status with easy to understand icons
• Features a patented alternator check which indicates if the alternator is maintaining battery level; ETL Certified for performance and safety

Klimfilt

Hi there. I'm in same situation like you with this Covid locks...
I've changed 2 times OEM battery by dealer (free of charge) because of this, and my car is diesel (which means higher battery start power needed). I've done some research and bought CTEK MXS 5.0 12V 5Amp. Test charge battery maintainer and it's awesome. Mercedes is using it by OEM charger, but only with changed brand in front of it. It's made in Sweden and it's the best maintainer probably. It has 3 test programs (Battery, Alternator and Start power) with them you can see is there any problem with your battery or Alternator. Of course if you don't need to test, you can buy the cheaper CTEK MXS 5.0 without test options (which is the same maintainer with few more options). In the kit you have eyelet kit which you can attach to your battery and leave it there for ages. Also it has option to recharge small batteries for motorcycles or small boats battery too. It has option for AGM batteries and non the last, option for Recond dead batteries. It can charge batteries up to 110 Ah and can support up to 160 Ah. And it's very small and can carry it with your backpack. The only negative for this charger is that you can't use it for jump starts.
When you attach it and select the program you wish, after it's completed the charger automatically goes on stand by mode and only support car battery when it detects falling from the optimal rates.
My car is sitting with him for 2 weeks since my New Year trip and there is nothing to worry about it.

teksurv

I have the same CTEK charger and it has worked great with both Benzes.

The G Man

If I remember right, you need to connect the ground first and then the positive when charging.
Does anyone where is the best place to connect the charger? Also, could the auxiliary battery be charge as well?

Thanks.

ua549

There is a grounding stud near the battery compartment in the engine bay. The positive connection is beneath a sliding door near same.

There is no aux battery in the W213. It uses a super capacitor that gets topped up by the car.

The G Man

Thank you for the information.

Hundens

Costco.

teksurv

As mentioned there is a grounding stud on the strut tower closest to the positive terminal. It's pretty obvious once you see it,

fleuger99

I use the same one for my 2020 E450. It works great. I got mine from Amazon for $90.

The_Judge

Based primarily on Klimfilt's recommendation, I bought the CTEK 40-206 Mx 5.0 Fully Automatic 4.3 amp Battery Charger and Maintainer 12V from Amazon. Used it for the first time today, connecting it directly to my car's nearly drained battery, which was fully charged within an hour or two. Very simple to use.

I also purchased the CTEK 56-870 Comfort Indicator Cig Plug which is supposed to allow you to charge the battery through the car's 12-volt connector (i.e., the cigarette lighter). Unfortunately my car has only one such outlet, in the read of the center console for use by backseat passengers (the outlets in the front seat area were not installed in my car — I have the wireless charger for my cellphone in the center console and nothing in the glove compartment the outlet was apparently by the perfume atomizer). I plugged the Comfort Indicator CIg Plug into the Charger and Maintainer, popped it into the cigarette lighter, and voila! It worked — for about 10 minutes. I didn't realize that the car shuts off power to the charger (and presumably other devices) after a few minutes unless the car is running. Not exactly optimal, so I'm resigned to opening the hood and connecting the charger directly to the battery. BUT I am keeping the Comfort Indicator CIg Plug as it can be used to test the battery's charge — just plug it in when the car is running and you get a red, yellow, or green light to show the level of the battery's charge. Handy for knowing when to pop the hood and hook up the charger.