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My 2014 CLA250 (no longer under warranty) started showing signs of a weak battery while cranking. I replaced the original Main Battery under the hood, started the car and got the Auxiliary Battery Malfunction message. I have a couple of questions relating to fixing this issue.

Is this a DIY project or something the dealer needs to fix?
If it is a dealer Fix, can I drive it to the dealer or does it need to be towed?
If I can fix this myself by replacing the battery...

How do you get the aux battery cover off? I can pop the clips and the cover will hinge up, partially exposing the battery, but the hinge at the top interferes with the bottom of the glove box, so I can't get the battery out. Is there a trick to getting the aux battery cover off? Are there any other pieces that need to be removed to get the battery out?

Should I disconnect the main battery before switching out the aux battery?

Are there any other components that should be replaced to clear the Auxiliary Battery Malfunction Message?

Thanks in advance,


Mark92131
 

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hello

Yes it is DIY pretty much did myself,

It is highly recommended to disconnect the battery terminal when doing anything in the car,

Open the carpet and it is easily seen, remove the plastic cover and unbolt the +- and lift the battery,
 

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I took it to the dealer (it’s safe to drive just the hold brake function and eco mode with start/stop should be off because they rely on the Aux. battery) . They replaced it for $245 and i was out in an hour or two so after they ran full diagnostics to make sure everything was ok and then they included the complimentary car wash and other stuff.
 

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I have just replaced my main battery. Looks a bit intimidating with the clear plastic vent tube and the powder charge on the positive terminal. Turned out to be pretty anti-climactic, took me 15 minutes. The battery terminals have 10mm bolts, and the battery hold-down clamp is a 13mm. The vent tube simple pushes into an opening on the battery, the rest of it was more or less like any other battery replacement, The hold-down clamp screw is a bit hard to get at, need a long socket extension, and the clamp was tricky to put back, PepBoys had 2 suitable AGM batteries (Champion) the H6 and an H7. Both show up as a fit in their computer. The H7 is perfect fit dimensionally, the H6 is a bit smalller (physically shorter, and a bit less CCA) than the original Varta. They had a 25% off web special, I asked for it in the store and they gave it to me. Cost w tax: $160. If you have the option, get the H7, same price. I see no ill effect, other than a few stored data items got reset (clock, date, etc) .
These suckers are heavy ( 50-60 LBS). If you plan to do the swap in the parking lot, make sure to have a 10mm, and a 13mm socket with a long extension. The hold-down clamp screw will probably be impossible to break loose with an open end box wrench. (Not enough room to get the necessary leverage). The aux battery can be had on Amazon for under $60 as I recall, the car is not complaining about it, so I left it alone.
 

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good o ' pep boys strikes again! when they have their crazy sales one can get the bosch platinum battery for <$150 ... not bad with a 4-yr full replace warranty, roadside help, etc etc etc
i run separate ground and power wires from a small battery to the terminals (and wrap them up) so i dont lose any settings
and yes this battery size is H E A V Y ... makes me want to look at the lithium replacements next time (since i dont use eco start stop)
 
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