Hello! Will be heading out soon to escape cold weather for 3 months for first time. Buying a battery tender. Dumb question.. how do you run the cord/cable into the rear battery - through trunk? And does trunk hatch stay open? Many thanks in advance!!

 

There are battery connectors in the engine compartment.
Alternatively some battery tenders have a connector that plugs into a 12v receptacle. (I've not tried it.)

 

My observations:

I have a tender that plugs into the 12 volt socket. Works spectacularly in my 2008 Porsche Boxster as the receptacles are "alive" even with the ignition turned off.

Tried it on my 2019 E450: did not work as the 12 volt receptacles turn off, are "dead" without the ignition on.

Has anyone found a 12 volt that remains "live" after ignition turns off? If not, then the tender must go directly to the battery.

 

For some reason my '18 E300 did not come with 12v sockets. I have a 110v ac socket. I use the battery connection in the engine compartment for the battery tender. I've considered installing a 12v socket, but haven't gotten around to it.

 

So far on my 2019 E450 I have found two:

• One in the front passenger foot well;
• Another in console between the front seats. You access it from the rear passenger seat. It is directly below the two air vents.

Neither is "live" when the ignition turns off.

Has anybody discover a third or fourth, one of which may be live?

 

Just a funny thought. I wonder how many people try and plug their battery tender into the 120v outlet in the car😀🔥. My e450 has a battery positive with a sliding shield over it and a negative terminal right under the hood. Simple.

 

Dear 2012 Merc amg:

12 volt receptacle:

As I posted I have one in the passenger foot well and another in the console between the front seats that faces the rear seats.

Have you found another and if so, where is it and is it live? I would like to use my tender which only provides for using the 12 volt receptacle. which must be "live". It does not have an extra set of wires to hook up directly up to the battery. I prefer to use what I have, rather than going out and purchasing another tender that will hook up to the battery.

 

So hook up to the front engine battery?

 

Yes just front battery. I just leave hood open never had a problem even after 6 months.

I use a Shulmaker maintainer. It’s 30 dollars at home depo. It has both hardwire or alligator clamps. On my truck I have it hardwired and just a simple plug in connection. On the Benz it’s easier just to use the alligator clamps

 

Thanks.

No other 12 volt receptacle besides the two I mentioned?

 

Nope that’s the only two 12 volt recepticals. My 2018 had one in the front ashtray compartment too. But the 2019s just where you said and the inductive cell phone charger

 

https://www.ebay.com/itm/0009822921-...8AAOSwm79ciXc2

Trickle charger came with 12V connector so you can hook up on your 12V in your trunk

 

This charger is made by CTEK for Mercedes. Putting the "Mercedes" name on the charger doubles the price.

If you want a CTEK charger, here is the one I recommend:

 

Thanks for all the info. Purchased tender online...

 

The one on Amazon look like is 0.8Amp Mercedes Benz Charger is 5.0Amp 12V

 

The .8 is a tender not a charger.

Hope this clarifies.

 

This is the 5-amp charger/tender you want. It's a later generation than the MB-branded one, and cheaper.

 

Glad your getting a maintainer Spencer. I too am a snowbird. I use this one available at home depo. Has never let me down. I like that it goes into eco mode and the green light slowly flashes on and off and I can see it with my video camera I have in my garage https://www.homedepot.com/p/Schumach...1248/207123536 know everything is alright. For $25.00 cant go wrong. I just put my car on it tonight as about once a month I give the battery a good charge as my Cabriolet sits around a lot and tends to get drain and then my cell phone alerts me the charge state is critically low.

 

i use the same one works like s charm. Its the same one most german automakers sell with their brand name. For those that don't realize it, a minder and a trickle charger are the same thing. A so called charger can provide much more current. A trickle charger charges very slowly, its best to maintain the battery topped off. Its current is insufficient to charge a dead battery since it would take too long.

 

My Schumacher will charge the battery although generally by the time it's reading Critical low it takes a day and half or so.

 

Just get an 8amp charger. Not much more money than what you previous mentioned.

 

I really caution using any charger or tender other than a CTEK. It's the brand that MB OEMs, although the MB-branded one is not the latest version. The CTEK is much more sophisticated than other chargers, like these Schumachers. It has a dedicated AGM mode, which uses different voltage and current profiles to fully charge our AGM batteries safely. That's very different than a charger that generically "can be used with AGM."

The CTEK MXS 5.0 takes the battery through eight phases:
1) Desulfation, using rapidly pulsed 15.8V, current-limited cycles if it detects this condition (usually on an older battery).
2) Soft start, applying 4.3A constant-current until the battery is charged to 12.6V.
3) Bulk charge, increasing voltage from 12.6 to 14.7, at 4.3A for a max of 20 hours.
4) Absorbtion, applying decreasing current at 14.7V, for up to 8 hours.
5) Analysis of condition, three minute load cycle with check that voltage does not drop to 12V.
6) Optional recondition phase, if selected, that attempts to salvage old battery by applying 1.8A at 15.8V for 6 hours.
7) Float, maintain at 13.6V with 4.3A.
8) Pulse, apply pulsed waveform between 12.7V and 14.4V (4.3-2.5A)

Phases 7 and 8 are the tender mode, and alternate to maintain or charge as needed.

All the voltages and currents I quote are for automobile AGM batteries. If the CTEK is set to non-AGM or motorcycle battery (AGM or non-AGM) different values are use. The voltages are also adjusted for temperature using an on-board thermistor.

The technology is this charger is amazing, and is designed to safely maintain an AGM battery in peak condition. It is not comparable to cheaper chargers that apply a compromise, but constant current at a compromise, but constant voltage regardless of battery type, state of charge, temperature, battery size, etc.

As far as I'm concerned this charger is the best accessory I've ever bought for my E63S.

 

Many thanks for all the insight!!

 

I've been using Shumachers for 20 years and never had any issues. I've left cars on them for 6 months at a time and they have never let me down. The only Battery I've had to replace was the smaller starter battery on my 2015 S550 Benz, but those are only good for so long anyhow, like 3 years. Glad these newer cars got rid of that setup, those were trouble prone. My 2019 E450 Cabrio is on my Shumacher now and it is fully charged, it took a day, but I don't care, there is no rush to charge it. I guess I'll put that car on it once every few weeks or so just to top it off, otherwise I seem to get a low battery critical message on that car as it sits around a lot. It is only a 1.5 amp maintainer. It's all I really need. I've had one like this one for the past ten years , it is multi stage charging, no problems. I have a newer one that is a lot lighter and slightly different design that I have on my Truck up north right now. It's about 3 years old and used 6 months at a time, no issues.

 

I'm glad it's working well for you. Just realize that 20 years ago we didn't have AGM. AGM batteries need a lot more TLC for long lives, which is why the charger/tender technology has advanced as well. There's no need to chuck a device that's working well, but if you're buying a new one it makes sense to go for the current technology. CTEK in Sweden pretty much defines the state of the art in this area.