Troubleshoot - Hybrid/Aux Battery Codes (P0A80/P3022)

Typically I see myself as a fairly understanding DIYer, but this one has me uncertain... Happy to add more detail as available to help diagnose this. Thanks in advance!

Backstory:

Replaced complete hybrid pack with NewPriusBatteries on a 2007 w/ 60k-ish miles about 2 years ago due to original hybrid battery failure. Aux battery (TrueStart) replaced about 3.5 years ago by dealership (prior to purchase).​

Situation:

There are about 20k miles on the battery over the past 2 years. I have been intermittently popping code P0A80 for a few months; no block code was presented at that time.

Initial diagnosis was to test the aux battery (false hybrid code positive), which showed a low charge. Aux battery was trickle charged for about a week (auto-stop charger), and went back up to decent "%" charge. Initial code went away for a week, then started popping again.

Next decided to spend the hours to pull the hybrid battery and voltmeter the cells (to my back's chagrin). All cells tested normal, and I also cleaned a couple bus bars of corrosion. Codes went away again for two weeks, then came back...

This time, I now have a P0A80 and (finally) a P3022 block code. However, I am still concerned if the aux battery might be the culprit.​

Questions:

• Do these symptoms clearly tell those with experience that it is for certain a bad cell, or possibly still the aux battery?
• Is it worth taking to the dealership for the $150 diag? (If the aux, they should warranty the 84-month battery.)
• Are there further diagnostics I can run (e.g. "duh, go get TechStream") or other recommendations?
• Should I pursue a warranty cell from NPB?

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