Help with P0AA6

Red triangle+other dashboard lights come on while driving. Turn off car, car can't go into ready mode, only accessory mode, can't put car into D or R.
Can reset by unplugging 12v battery cable for a few minutes, replug, car starts and drives normal for about 5 minutes, red triangle with loud beep comes back on but I can still drive fine until I turn it back off.

Bought obd2 and used dr prius app. Code read p0aa6.
Did research and uncovered hybrid battery. First thing i saw was corrosion on all of the nuts holding the orange harness against the cells.
A lot of corrosion on the main service plug wire. I removed all the nuts + small metal plates holding the cells and cleaned them.
Tested all cells with a multimeter using DCV 20 setting, all cells read at 7.5 and above.
No fluids or leakage anywhere.

Replaced everything and red triangle still shows. Opened everything back up and noticed there's still a little bit of corrosion on the service plug wire that I can't really clean off.
I tested the 12v battery with the multimeter and it's reading at 12.3v with the car off and with car on its around 11.4.
I've already changed out the water pump and replaced fluids. I know about the mini vci but am trying to hold off on buying more things if I can.
Been at this for a week, help would but appreciated.

 

The plug itself is in good condition. The wire that's attached to the plug towards the ends where it meets the cells has a bit of left over corrosion that I can't really scrub off. I was wondering would that little bit be enough to cause the problem? If so, I'll just change that out and give an update.
Or would the problem be because of my 12v battery?

 

Sheesh, I didn't know that. Buying a vci cable now.