Thought I'd add my experience with the AAA battery installed in May, 2020. That was approx. 12,000 miles ago.

2011 S550 has 160k miles and runs great. Have replaced both front air struts at 125k - 150k. Also both control arms and bushings, also the two motor and one tranny mount. Tranny flushes at 75k and 155k. New radiator at 140k

Started getting red battery icon on dash about a month ago.

1) mid April, 2022. Called AAA , they sent Battery tech, who came out and said battery is fine... must be something else generating the icon.

All MAY 9, 2022

2. May 9, 2022. Having still gotten red battery icon off and on for the past three weeks, now the car, turning into a commercial driveway, turned off. Power steering went out just before... Five minutes later I was able to restart the car, and moving slowly forward, fightng the wheel like it was a manual steering, as it is pulsing on and off, I get it into a parking spot.
3. May 9, 2022: Called AAA , they sent Battery tech, who came out. Had me crank the car, took his readings, and said battery is fine... must be the alternator. Oh crap, $1200 or so, but OK, ,old car at this point.
4. May 9, 2022: Called AAA roadside service, on hold for 20 minutes, connecting 4:27. Ask if I can get a quick tow to MB dealer two miles away, which closes at 6pm for a courtesy car. They say no, best they can do is 90 minutes, about 6pm. OK. I called at 5:50, not seeing any update. On hold for 15 minutes, line goes dead. Called back, asked for suupervisor, informed the tow truck might make it by 7pm
5. May 9, 2022: Tow truck arrives 6:50pm. Asks what battery guy said, I explained, also explained car dying and Power Steering going out. He said -- tell you what, you don't need a tow, you have a bad battery. He asked if I started it for the Battery Tech. I said yes. He said...try starting it now. click, click, click, click, not start. Tow driver says --See, you got a bad battery, I don't care what the Battery Tech's readings were. Let me jump you, drive around a couple of minutes, and if everything is OK, have your son in law (called him for a ride for after car left on flatbed) follow you while you driver yourself home and call for another AAA Battery tech and *insist* on a new battery. (this dude KNEW somehow the AAA battery for W221 doesn't produce what the car needs, regardless of how it reads on their little device.)
6. May 9, 2020: Battery Tech arrives 7:45pm. I asked for escalation, got a supervisor in Batteries, and was told if the handheld reader says the battery is fine, they will NOT replace it under warranty... company policy. Battery tech reports Charge is Good, Cranks normal and Charges Normal. Leaves me the printout and apologizes for not being able to be of service, and cancels the call.

All May 10, 2022

7. May 10, 2020: Called AAA tow to again take it to the MB Dealer, MB of Laguna Niguel. After 1:05 of waiting, I said screw it, I drove home I can drive it to the dealer, and took the risk of losing steering again.
8. May 10, 2022: Service advisor, hearing all the details, immediately says... It's the battery. We've had to replace AAA batteries on S class sedans that AAA says are fine many times. When we hook them up to our system they show they don't produce the (can't remember word...current?).
9. May 10, 2022: SA calls and says yep, Battery failed the performance test. I approve battery replacement.

My conclusion is either that the AAA battery currently being installed into W221 is inadequate to supply the current under certain stress conditions, or AAA has bad quality control... but I don't think it is QC because why did 3 AAA battery techs all say the battery measures within spec?

Aside from learning that AAA batteries for W221 (around $240) pass the AAA handheld device but fail the dealer's more thorough test (dealer recommended by AAA roadside service!), and don't function at a level the W221 needs, I'm also learning if you need a tow in Orange County, CA form AAA, expect to wait 1-3 hours. But the worthless battery techs arrive within 45 minutes... cuz they have a product to sell.

Will update when I pick up the car, but it has to be the battery b/c the dealer went through all the codes it threw and all the faults were for insufficient voltage.

 

What brand does AAA install, what size, and what rating?

 

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I don't know who manufactures it, but it is labeled AAA. the size is the one that AAA specs for 2011 Mercedes S550,
Interestingly, the MB Service Advisor said MB batteries are about 2" larger than the one AAA installs into the S Class.

The AAA Battery Tech test printout shows: voltage 12.18. Rated: 1350 CCA, Measured 1334 CCA. 71F, Cranking voltage 11.19V, Charging Result No Load13.33, Ripple voltage 32 mV

 

so its a later car circa 2011 and the battery light on the dash doesn't go away ?

if so this is normal failure and its not the batteries and Merc diagnostics doesn't help much - loads of posts on this issue

 

Yes, a 2011. The battery light wasn't the issue though. It would be on some days and not others. the problem was that the power steering failed, and I believe, but don't know for sure, that when that happened the computer shut off the motor. I will get a more clear answer when I pick up the car in a couple of hours, but the reason the PS failed was because its control unit wasn't getting enough voltage from the battery... could be wrong, will report back.

What is puzzling to me is that after I started the car 45 minutes after the shut off, when the MB Battery tech arrived, it started. He left. Again 45 minutes later, while waiting for the tow, I wanted to reposition the car to be easier to load, and the car wouldn't start.. tick, tick, tick, and the dash flashed all sorts of weird messages and bllnked on and off. Then the car wouldn't turn over (tick tick tic,, tick)...again when the AAA tow truck arrived an hour after that.\

I can't believe that when the mercedes diagnostic computer reads error codes that the failures were for insufficient voltage... that those diagnoses "don't help much". But hey, anything is possible.

 

OK, as promised the service notes:
------------------------
16007 Found 12 volt battery to fail midtronics test upon bringing into service bay. Found vehicle had a delayed start. Viewed charging voltage via the instrument cluster and found ccharging voltage OK at 13.9 volts. Measured 12.5 volts at the starter. Locked vehicle and closed hood locks. Measured 0.003 - 0.004 AMP draw on the battery. Current draw within permissible range.,

Connected SDS and battery maintainer and performed a quick test. Found multiple low voltage codes in multiple control units. Installed new battery, performed another quick test, and cleared all stored codes. Test drove vehicle from 160,054 to 160074 miles, did not duplicate customer's concern about power steering failure and vehicle shutting down while driving.
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So, I'm sticking by my conclusion that a AAA battery spec'd and installed into my 2011 S550 (see above) tests good to AAA handheld reader, and fails Mercedes more thorough test. Further, said failure caused my power steering to fail, which caused my S550 to turn off the motor while driving.

Bottom line, AAA provided me with a dangerous battery, plain and simple. They appear to have no way of diagnosing it, and refuse to replace it under thier 36 mo. replacement policy because three different AAA battery tech visits showed the battery to be healthy.

I would not recommend anyone install a AAA battery into a W221 2011 S550. Imagine if my car had turned off due to insufficient voltage from a AAA battery to the power steering control unit (tested by three different AAA battery techs), on a blind corner, and somebody rear ended and seriously injured both of us.

 

When I first read the post title, this came up in my mind and I scratched my head. Is this about the Entertainment Remote Control?
lol...I am so wrong.

 

Ford focus with electric steering goes wrong - Ford cure new steering rack - but often behaves again with a new battery....

Modern cars do odd stuff with electrics - and seem to have designed in fun....