LALALAND

Does anyone know how to charge the auxiliary battery in the trunk? I just bought a Ctek mus 4.3 for my other car that I only use to travel to rough neighborhoods for good food. Don't care about dings,scratches, or jacked on that car. Had to charge that battery as I only use it like once or twice a month after I got the E.
Can I use the motorcycle icon(1.2Ah-14Ah) mode to charge the aux battery on the E? My car hardly every activate Eco stop, but I'll still like to have hold and hill assist available (both use aux battery). I read a lot about 2014 that show Eco icon in yellow(need to charge), but where in the multifunction display as I never seen it before on a 2015. It's either ECO in green when the engine is cut off or nothing(not shown in the MFD).

Thanks!

rorywquin

You car probably has AGM batteries (but check for yourself).....in my car, you connect the charge leads to the jump start points (it is somewhere in the owners manual - check yours) and set the charger to the appropriate (AGM ??) mode.

kajtek1

I would never put a charger on battery hook up to the car.
I have high-tech Schumacher charger that displays charging voltage and just lately discover that thing lie to me. When charger did show 14V, additional voltmeter went over 15V.
The trunk battery has 10MM hex bolt on clamp if I remember it right, so taking it off takes just seconds.
That said I don't think you need to put charger on it. I had my W212 (and other cars) sitting for 2 months this summer with disconnected batteries. After that period I topped off the main battery but did not bother with aux. It hold the charge just fine.

rorywquin

The MB instruction manual for my car says to use the jumper points - not sure about yours.

General consensus is that it is better to keep your batteries topped when the car is not in use. Cranking batteries do not live long when repeatedly deeply discharged. Unless you have deep discharge batteries fitted.

After charging and immediately after you remove the connections the voltage will be a couple of volts higher than what the true reading is (float voltage) ...you need to leave the batteries for a couple of hose before you check the V on a meter.

CTEK (Mercedes, Porsche etc)......is one of the best chargers on the market.

kajtek1

Jumper points lead to main battery.
Main point of not hooking up charger on the car is that lot of chargers can go as high as 18V and as I posted even the computerized chargers are not good solution.
What 18V can do to your car computers is something that I am not willing to find. out.

rorywquin

I'm sure you know better than MB thanks for the information.

thefisch

Yeah, I had a Schumacher that went up to 15.3V. Got the ctek instead and it keeps it at or below the MB recommended 14.3v. In fact the one MB sells looks like a rebranded ctek and you can charge while connected to car.

rorywquin

Yep - it is a rebranded CTEK

mnje350

Been using the Ctek on my 2010 because the car will sit for a week or two before I put maybe 50 or 100 miles on it and the battery seems to really like it. I had to replace the factory battery after two years. This one is still going strong. 5+ years. This car does not have the Aux battery though.