Had my car in getting re-work done from the botched airbag install (see my other thread) and was told that the auxiliary battery that powers the electronics whilst under ECO shut off has failed.

Nearly fell out of my chair when I heard the quote to repair of $560. Easy pass for me since I generally hit the button to disable the ECO system anyway. But I did have a couple questions.

-Is there a place to source this batter other than the dealer? I checked some of the usual parts stores online and didn't find anything. I figure it might be worth replacing at some point if I do it myself.

-My SA told me that "batteries are not covered under CPO warranty." Didn't question that until I was reading through some other threads on here about people have their main batteries replaced under warranty.

 

Just take it out of the car.
Permanently disables the stop/start function and doesn't effect anything else or cause any problems.
Or, if you are feeling a bit lazy, simply disconnect the secondary battery earth lead where it bolts to the floor of the boot/trunk and tie it up out of the way so it can no longer connect to the body of the car.
If you really must get a new secondary battery then you want an Exide EK151, see this thread on another forum: Start Stop Auxiliary Battery

 

You can definitely buy the battery much cheaper and fit it yourself.
Re the warranty, the factory warranty will cover a defective battery. But Cpo is not a warranty and has a lot of exclusions for wear parts eg bushings, seals, etc. It typically won't cover a battery which will fail over time