C-Class (W204) 2008 - 2014: C180K, C200K, C230, C280, C300, C350, C200CDI, C220CDI, C320CDI

Battery questions -- with start/stop

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Old Sep 12, 2018 | 08:20 PM
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2013 C300 Luxury
Battery questions -- with start/stop

We have a 2013 C300 gas with the "ECO" start/stop "feature". I need to do some work with the battery disconnected, and frankly it's getting near the age of replacement. Answers to the following questions are at best scattered:
-- Any reason I can't just disconnect the battery the usual way? There's a circle-slashed pictogram of a battery jumping into the air, and a book next to it. What's that mean? The manual just says you'll have to reset the clock. (We don't have COMMAND.) I've read elsewhere that you must re-cal the steering angle sensor. Anything else?
-- There's a baby battery (I think) in the trunk. Must that also be disconnected to truly remove power? (I need to pull the steering wheel and airbag.)
-- Where do I find the radio code? (Car bought used, but have the manuals--no code card.) The dealer service invoices have an entry "MO:xxxxx" -- a 5-digit number. Is that it?
-- With start/stop, are there any particular constraints on selecting a new battery? (Other than the obvious size and capacity)
-- On some German cars (ahem) a new battery must be "registered" with the electronics. Is this one also like that, or is it like every other car I've owned--connect up the battery and go?

Thank you! Let's make this a useful summary for the later W204s with start/stop.
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Old Sep 13, 2018 | 05:49 PM
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2019 S560, 2015 Honda Civic Hybrid
Can help with one of the questions ... I disconnected the big battery (under the hood) to change my steering wheel/airbag and did not get a code afterwards, so that's one thing you don't have to worry about.

Also, on my car anyway, the "radio code" we're all used to is not an issue, the dealer told me the radio actually reads the signal from your key to operate (pretty slick idea!). So two things not to worry about.

I'm wondering about the function of the "baby battery" in the trunk. I accidentally disconnected it for just a second or two and no ill effects noted. But not sure what it's function is, nor how it relates to specific systems/functions of the car.

Good luck, post what you find out ...
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