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So my 2014 CLA Sport only has 50K miles on it (thank you COVID) and my original AUX Battery still has not failed and displayed the DASH ALERT yet, however by reading info in these forums and trying to be proactive - I bought another AUX Battery with the intention of replacing mine as soon as I had a chance. After all, 8 years have gone by and surely this battery is gonna fail...and most likely at the worst time.

So after learning the cost of the OEM batteries, I decided to buy a new battery from a different brand after researching the specs, size, and other info just to be sure! I chose this version on Amazon (you can do a search for it):
Chrome Pro YTX14-BS iGel Maintenance Free Replacement Battery with Digital Display for ATV, Motorcycle, Scooter, Snowmobile, and UTV: 12 Volts, 1.4 Amps, 12Ah, Nut and Bolt (T3) Terminal

I even kept it charged fully with a trickle charger.

Then last week, I noticed while driving and stopping at intersections - the ECO Setting did NOT turn the car off, like I was used to it doing. I looked this up and saw this is one of the first features to stop working before the AUX Battery dies. Still though, NO AUX Battery Failure alert yet.

SO tonight I spent some time in the garage and made the move to replace that battery.

As most sources have shown online - I pulled the carpet away, it was located below the Cabin Filter. I removed the cabin filter access cover, which allowed me to REMOVE the access cover to the AUX battery below it. I removed the terminals to the old battery, removed the vent tube - and pulled out that old Merc OEM battery.

The new battery I purchased had an extra bolt and bolt holder included in each terminal port. I now know why! While I didn't need the bolt, I DID NEED the bolt holder so the 2 terminal wires would grab and allow me to tighten each to the battery. I tightened each terminal and before cleaning up - I decided to turn on the car and check for any alerts etc...

NO ALERTS - and the windows, anti-slip, radio, etc...did NOT need any type of setup or calibration.

I cleaned up and have been driving with it ever since without any issues.

All in All, if your AUX battery is more than 5 years (maybe 6 or 7), just replace it before you get the FAILURE ALERT. It doesn't take long and you can save a lot of money buying this $60 battery vs the Merc cost and Labor for them to replace it for you.


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