What make and model charger do you own?

 

I use the CTek maintainer if I'm not going to drive the SL55 at least once a week. It is the type that is reported to work very well with the Absorptive Glass Mat (AGM) battery in the trunk of these cars. This type battery is apparently very sensitive to charge rate, overcharging, etc.

 

I have used CTEK on several of my cars for at least three years. I just leave it plugged in all the time. It does the rest. I maintained one car for almost two years with it. Started the car up every month or so. Battery did fine.

CTEK is the best.

 

I bought and use CTEK MUS 4.3 POLAR only for the fact my ride sits in carport and car covered with the cold New England winters. It's rated to -22F and believe me I'm not in Florida anymore!

ctek is your best route to take!

 

Well here's the one i use on my other cars. Works fine, charged all batteries i had.

Is there a special one i should use?

 

Is there a special one i should use?

The charger that MB sells is a rebranded CTEK. That's good enough for me, so I bought a CTEK. It's cheaper than the MB one.

Regards,
Don

 

CTEK's here...several. Smart chargers that handle almost every charging scenario. I use them for waverunner AGM batteries...connected months at a time. Mark

 

Do you guys leave the battery connected to the car or disconnected when charging? This was my second question

 

I leave it connected to the battery and plugged in. Until I decide to move it to one of my other cars. If I had more, I would leave them all connected all the time.

 

The CTek has a snap together 'connection', and two options for attaching the wiring to the battery - one is eye connectors and one is alligator type clips.

I hard wired the eye connectors to the battery (required soldering in some wire extensions as I recall), and the pigtail from that has the connection for the charger, snaked up and into the back right corner of the trunk. Just open the trunk, make the snap connection and plug the CTek into an outlet. I leave the trunk open about an inch, so I don't 'forget' and try to drive the car without first disconnecting the charger!

 

I'm going to have to do that. I drove out of the garage with it still plugged in and was driving down the road with the charger trailing behind me :eek

Wife and kids had a good laugh. Wife was wondering why the extension cord was out in the alley along with the fan that was also connected. Sheesh...

 

I have the CTek terminals bolted onto the battery with the eye fasteners, and fished the wire through the bottom of the left corner trunk comes out under the shield behind the left rear tire. Just pull it out when I want to connect it to an extension cord, and tuck it back in when ready to drive. The charger is connected all the time to the battery. Never had experienced electrical problems either plugged in or not plugged in.

 

I never remove mine. Just plug the cap on when disconnected from the charger.

 

FWIW I use a Battery Tender Plus with no problems. Also rated for use with AGM batteries. I have it hard wired to the rear battery with the supplied connector. Then its just a quick disconnect when the car is driven.

 

Good point !

The BatteryTender Plus is open to the elements. I would not recommend it for outside use. My car sits in a climate controlled garage.

 

On your SL55, did you trickle charge both batteries, or only the one in the trunk?

 

On your SL55, did you trickle charge both batteries, or only the one in the trunk?[/QUOTE

I use my Battery Tenders all the time on my limited use cars. During winter I Battery Tend both the start battery and service battery on the Benz (two separate Battery Tenders). In the summer months I continue to keep the cars plugged in perhaps out of habit after their use. The start battery connection is a pain on the Benz so I only plug the start battery in if I plan not to drive the the car for more than a week or so. Even my lawn tractor has a Battery Tender!
I've never had a problem with any of my vehicles electrical systems that I could blame on a Battery Tender and I've been using Battery Tenders since the late 90s.

Speaking of batteries. Does the battery that powers the key FOB of my SL go to sleep and not try to communicate with the car when the FOB is stationary and within communication range? I ask because the FOB in my Jag does go to sleep. My three bay detached garage is very secure and well alarmed :wink and I'd sure like to be able to just leave the Mercedes key in the glove box during the summer months rather than repeatedly say, "Damn, I left the key upstairs in the house in my jeans ----- again!" Where I live car theft is pretty much unheard of. Any car thief in or near the village where I live would go for my locked and alarmed truck that sits outside before even looking at a shinny MB or Jag.

 

I use a maintainer - NOT a trickle charger. Only connected to rear battery.

Gary

 

Same here. I also have a battery tester which checks the battery's condition. You input the CCA info with the battery type etc, and it gives a report on the condition. Great tool! Easy to use.

 

This is the tester I use...

https://www.amazon.com/gp/product/B01M0ARG3X/ref=ppx_yo_dt_b_asin_title_o08__o00_s00?ie=UTF8&psc=1

 

If you have KeylessGo, the SmartKey does not go to sleep. It has a very low powered circuit that is always listening for the car. When it recognizes that the car is nearby (within 3 meters) it will begin to transmit. The batteries in the SmartKey will last for at least a year, probably two or more this way. However, if you leave the key in the car, or within 3 meters, it will constantly "talk" to the car its batteries won't last very long.

 

Wonder what the FOB and car would do if the FOB were 'hiding' in an RFDI proof bag inside the center console? Both the car and the FOB are always kind of looking for each other to shake hands but the car has a very large battery out back to power what probably is a very efficient transmitter. Service battery depletion shouldn't be much of an issue. As you've stated, not so the FOB.
You also mentioned that it's search range is around 9 feet. My work bench in my garage (3 car) is certainly more that 9 feet from the Benz which makes me wonder if that's far enough away to not awaken it. If it is a key rack my save me the frustration of returning to the house to grab my key :smile. But how can I tell if that distance is far enough? I know that any button push on the FOB is a 'wake up call' because an awake FOB certainly transmits more than 9 feet. Long short, how can you tell if a key FOB is dormant?
If all else fails I guess I could try to remember to put the key in my pocket before leaving the house but there's no fun in doing things the simple way :grin

 

I have a CTEK 4.3 and I leave it plugged in all the time. I've had no issues with it whatsoever.
Once it detects that the battery has lost some charge. Then the charger kicks on, tops off the battery charge.

 

KeylessGo is a very low drain on the vehicle battery as the constant signal that the car transmits is very weak, hence the approx. 3 meter limited distance. Of course it does require power so it's just one of those things that will very slowly drain the vehicle battery as the car sits unused.

Pressing the button on the fob to lock/unlock is a totally different function. This circuit in the key is totally unpowered until you press the button, then it activates a higher powered transmitter that the car listens for. It's a one-way communication from the fob to the car. It does usually work at a much greater distance than KeylessGo. Mine works at probably 100 feet on a good day. That won't drain the fob's battery (unless you use it) but the car's antennas being constantly powered to listen for the signal is just another very tiny but constant drain on the vehicle battery.

If you put the SmartKey in a "Faraday Cage" then it would not wake up and start transmitting via KeylessGo. Honestly, your best bet is to just hang it ont he wall, 10 feet from the car.

 

Once you're in the car and have started the engine by pressing the KeylessGo button on the shifter (key has been in your pocket the entire time) does the fact that the car is running change the FOBs broadcast program? I would expect that both the low power and full range transmitters would be awake and broadcasting with the vehicle under way and would be consuming key FOB battery power by being active? I also wonder if keyless entry works if the key is in the car. I don't recall reading that you can or can not lock your key in the car.
I'm going to put new batteries in my key FOB and record how long it takes to receive a 'key battery low' notification (because I've purposely left my key inside the car rather than in my pocket) Ever wonder how many keys have seen the insides of a washing machine?
I'll let you know my findings. Hopefully my findings will add a little 'tidbit' of information to your considerable knowledge of these cars. Besides, my curiosity is killing me. Thanks for all the replies.

 

Yes, with the key in the car when driving, there is a constant communication. Really, anytime the key is within 3 meters of the car, it communicates. Actually, it's more like 1 meter, but it can be "up to 3 meters". You can test this by starting the engine and then removing the key - you'll get a message on the instrument cluster's MFD.

Once the key as been used in the ignition (either inserted into the ignition or the KeylessGo Start/Stop button has been pressed), the RCL (i.e. fob buttons) functions are disable. So, you can't lock or unlock the car with the fob while the engine is running. Or for that matter, you can't lock or unlock the car with the fob with it in the ignition switch.

As for accidentally locking your keys in the car, with KeylessGo, that is very difficult. First of all, the driver's door won't lock unless it is closed, so you'd have to do this via the trunk or the passenger door. And you'd not be able to do it via the KeylessGo lock buttons. They won't work if it detects a key in the car. You'd have to leave the passenger door or trunk open, press the fob lock button, toss the key in and close the door/lid. Even without KeylessGo, you really have to try to lock your key in the car. Probably the most common way is that you have the car locked, you walk up and press the button to open the trunk. You then reach into the trunk key in hand, and drop it in there, then close the trunk lid, which will automatically re-lock.

 

Good info Rodney. Thanks.

As for my battery life experiment, I think I''ll leave the drivers side window open and the key on the driver seat rather than leave all the windows up and key in the console just to guarantee key access. One never knows when ones car wants to have a little fun and say 'bet you didn't know I could do this'. I only have one key at the moment and taking chances making the only key I have not accessible isn't on the menu.
Might be smart to visit a Mercedes stealership in the very near future and get gouged ordering a second key.

RB

 

Just for info, I live in coldest Canada and my 07 SL, owned from new, is garaged from November to April every year. I keep the accessory battery healthy during storage with a constant 13.8V output from a high quality charger. The starter battery has never required charge through even the coldest winter and will start the car in April after 6 months without any problem.

 

Starter battery is completely isolated from the rest of the car. To prolong its life give it short charge once a month. It will circulate electrolyte and help junk fall off the plates and sink to the bottom.