First, I am concerned about the 270 volt drive battery. I don’t think that using a 12 volt battery charger is a solution for keeping a 270 volt battery optimized for long term storage. Keeping the 120v Wall charger plugged in would make more sense, but dealer has no idea if this is a solution. I sent an email to Kia, so far no response.
My experience with lithium ion batteries in my RC planes is that they should be stored at 50% charge and, even then, they will eventually discharge and fail after being stored for longer periods of time.
Dealer “verified” the Niro doesn’t have a 12 volt lead acid battery (said there was a separate 12 volt Lion battery), but my experiences with dealer accuracy is poor. Also, I sometimes get a “Aux battery” has been recharged message on startup...which really has me concerned about long term storage.
Surprisingly, Tesla has a 12 volt lead acid battery, go figure. It is there to power the infotainment system from what they say.