For AGM starter batteries in both the C217 coupe and W222 sedan, WIS advises not to test it at the charging terminals under the hood due to possible faulty readings. This dictates that testing must be done directly at the battery terminals requiring removing trunk paneling. What a joke. Can anyone shed any light on this?

 

No one ever had their battery tested?

 

Not sure about where to test, however Dealer wanted $175- to test. I declined, however when they completed another service the same day, it stated Battery Good. Its not a simple test, they have special equipment that they must go through specific load processes and receive a printout of detailed testing. No longer just Volts and Amps. My battery id 7 years old... I do use a maintainer during the winter months when its not driven. I had to replace the AUX battery once, DIY job.

 

Ideally the battery is disconnected, fully charged and then tested. Given this has been a year of less travel for many, throw a CTEK, NOCO, Solar, BMinder, etc... on it once in a while.


Otherwise test at the battery, ~12.7 VDC is fully charged for AGM (checked after charging and disconnected for a few hours) and battery should not drop below 10 VDC while starting. If you have a tester, pile or capacitance give those a rip as well.

What makes you suspect the battery or desire to check it?

 

Thanks, I know how to test a battery. I just like to check my cars' batteries periodically as they don't last long here in FL due to the heat. Mine are usually toast after 3 years and this is after years of experience with hot FL temps and batts as I've lived here since '69 and have been thru many of them with various cars. Perhaps the AGM type will last a little longer.

I just don't want to get stuck some place with a dead one (especially getting a call from the wife at the mall.) And I'm not wild about spending 1/2 hour or so removing and replacing trunk paneling to access it for testing. But I guess that's why MB wanted $175 to test the above poster's. Why they did this is beyond me.

I think the reason for this, though, is that the starter and aux batteries are tied together.

Anyway, I'm hoping for a shortcut but don't think there is one.

 

For $175 you might as well just change the battery... MB’s charging scheme on newer cars doesn’t help with battery life.

You could also install a charging pigtail/port and/or monitor in the trunk for easy access in future.

Or just buy a battery every few years, and don’t worry about it...

 

Starter and Aux Batteries are not tied together. If you connect a trickle charger to the Main Battery, it will NOT charge the Aux Battery.

 

Thanx...

Why is it then that you can't obtain a battery's condition from testing it at the charging posts?

 

[QUOTE=bmwpowere36m3;8332761]

You could also install a charging pigtail/port and/or monitor in the trunk for easy access in future. /QUOTE]

Thanx...

Not sure what you're saying here. Is there something available where the posts could be added (extended thru the paneling) to where they are accessible for batt testing and can be protected against shorting when not needed?

 

[QUOTE=Jud Chapin;8333036]Yes, there interfaces available... but it would depend on how you test the batteries. Are you doing simple voltage checks for SOC, capacitance testing, or load testing? In addition to you use any battery maintainers?

 

[QUOTE=bmwpowere36m3;8333064]
Load testing...

 

[quote=Jud Chapin;8333065]With a carbon pile, right? That's going to be tough because your pulling a few hundred amps... They have dedicated battery monitors, going rate is ~$200+ like this:
Another option is to install an panel mount adapter like this:



This can be used to hook up a maintainer AND one could make an adapter to perform voltage and/or capacitance checks. You could make test point for load testing, I'd envision using a 2 pin battery disconnect, appropriate gauge wire and terminals... that just seems like total overkill though. Example:

Personally I'd spend the 30 minutes once a year to check the battery with the load tester, or keep a lithium jump in the trunk or AAA.

 

Thanks so very much for your time on this. It's really appreciated. The lithium jump sounds like the answer. Can you recommend one?

 

Don't know much about these jumpers but this one seems highly rated...

https://www.walmart.com/ip/NOCO-Boost-Plus-GB40-1000-Amp-12-Volt-UltraSafe-Lithium-Jump-Starter-For-Up-To-6-Liter-Gasoline-And-4-Liter-Diesel-Engines/46605770

Don't really need one other than for jumping but definitely want it in a case of some sort.

 

I have a NOCO GB70 that I use around the house to jump anything from a motorcycle to a skid steer.

 

That one's a lot more powerful at 2000 amps. If you're happy with the brand, I'll pick up a couple of the 40's. $100 seems to be the going price for these.Thanks again.

 

Just ordered a couple from Walmart, $100 a pop with free next day delivery in case anyone's interested. Sorry Amazon...Too slow w/o Prime.

Thanks again for your help, bmwpowere36m3

 

You need to be careful on your question.

Main Battery can be trickle charged with CTEK or Mercedes sells the same unit manufactured by CTEK.
The AUX Battery is a totally Separate Battery that is isolated from the main battery. It will only trickle charge when the car is running. It will require another maintainer.

 

I don't know of any reason why not. The cables run directly to the trunk battery. You can check Sitting Voltage and Running Voltage with a meter.

In general, you should never see a battery sitting below 12.3ish After starting the car, you should immediately see 14V+ In newer vehicles, a management system takes over and will determine how much and when to charge the battery, this also saves fuel as there is not a constant drag on the alternator.

 

ALL I know is that WIS says you may get faulty readings and to test the battery directly.

 

I like this unit.
Amazon.com: CTEK (40-149) CTX Battery Sense - Smart Battery Monitoring on Your Mobile Phone: Automotive

Amazon.com: CTEK (40-149) CTX Battery Sense - Smart Battery Monitoring on Your Mobile Phone: Automotive

 

All due respect, but I'm not sure why you think I need to be more careful with my question. It's pretty explicit and has nothing to do with charging the starter battery, only testing it. FYI, I have 2 CTEK MXS 5.0's, 1 for each car.

 

[QUOTE=bmwpowere36m3;8333131]Where did you locate that CTEK part in the photo. I could not locate it. Its a great solution ( Permanente connection point, nice and clean )

 

I believe this is it.

https://www.ctek.com/uk/products/car...tor-panel-1-5m

 

Received my 2 NOCO GB40's jumpers today and was disappointed in the bag provided for storage so I picked up a couple of these..




Much better ...