2015 Engine Revving When off of accelerator pedal

Reving after releasing gas. | PriusChat

That thread might at least be worth a read.

For the Gen3, the battery intake is between rear seat and passenger side door. about elbow area if sitting
The kind young @Mendel Leisk can add schematics of the single bolt if necessary,
but check at least the intake to see if you need to clean it out and the HV batt fan.

The original 12v battery, could also check that.
-best to pop hood, and let rest overnight then touch jump points with multimeter to see resting voltage.
The vacuum lines would worth be looked at too.
70k miles in 2 years? wow that is a lot...just to add...

 

To the OP, Did you read the thread PriusGuy32 linked?
I have read that thread and some other one where the culprit was that EVAP vent valve. That part is very cheap (under $100), easy to replace.
I would check that one before spending several hundreds on a 12volt battery replacement.

 

Just read the first post and glanced over some other posts including the one with the DTCs and I am sure you have your EVAP purge valve stuck open. Hit it with a tool and the issue will probably go away.