2006 w/ P0A80... grid charger?

First off, hello. Great forum here!

I've been looking for a 2nd Gen Prius for a while that needed some love (my hobby is reconditioning cars) and I recently bought a 2006 Prius with ~160k miles and a P0A80 code. Red triangle, running poorly, etc. I bought it at the right money that if I have to replace the whole battery, I'm ok with that. BUT.... I'd rather tinker with it for a while to see. My first hybrid car (of over 200).
I noticed some oddness with the fuel gauge and the display, and discovered that the 12v battery was bad, 11.3v in ACC mode, so I got an OEM battery, topped it up to 12.8, and installed it.
First start up.... no P0A80. Drove around a bit, and the code came back. The car goes into limp mode (I have an ultragauge plugged in and can easily/quickly reset it. When the code isn't live, the car seems to run fine. Power is ok, etc. Over the last week or so I've been driving it around and the code (and limp) is getting less frequent- from every time I drove it to just once yesterday, in maybe 10 drive cycles.

Anyway, I assume the HV battery is getting weak and the bad 12v added to the poor performance, but the HV pack is going to need attention. Does this sound like a good application for a grid charger of the Hybrid Automotive type?
It seems like swapping out the weak modules and doing a few charge/discharge cycles might breathe a little life back in.
Thoughts?
Thanks!

 

I've ordered up the Techstream, so we'll have that soon for more fiddling. The car definitely has the symptom of the battery charge level fluctuating rapidly.