Help diagnose - warning lights, P0A80

I am having an issue with my 2007 Prius, 167000 mi, original Hybrid Battery. I believe the hybrid battery is dying, but would like to confirm that before I move on to expensive repairs.

Main Symptoms:
Drove car approximately 0.5 miles and had many lights appear on dash, including:

• Red Triangle of Death
• Brake system warning light (amber, circle with exclamation point, not the tire pressure light)
• VSC
• CEL (check engine light)
  
• Red car light w/ exclamation on touch screen display

Code from standard OBDII reader: P0A80
Cleared code, which cleared all lights. Code and lights returned on my next drive.

Other symptoms:

• Reduced mpg over last 6 months (down from 44 to 37 mpg)
• Hesitation when stepping on throttle when engine is cold
• Hybrid battery display/consumption shows that hybrid battery will charge fully but also rapidly discharges (e.g. 10 minutes in the store is enough to fully discharge hybrid battery)

Troubleshooting steps:

• Replaced 12 V battery with brand new battery
  • Previous battery was 6 years old and failed battery test (measured 11.84 V)
• Confirmed gentle movement in inverter coolant tank
  
  • IG ON but engine NOT RUNNING
• Thorough cleaning of throttle body plate, butterfly valve, and MAF sensor
• Note: the car likely will benefit from replacing the PCV valve, hoses running to the throttle body, and replacing spark plugs, but I don’t believe those are the source of my issues

Is there other troubleshooting I should do? I’m guessing this is a textbook hybrid battery failure, and time to fully immerse myself in the forum to explore my options. Many thanks!