HV Battery error

I'm brand new to hybrids and Prius. I bought an 08 Prius that has an HV battery issue. I have a VeePeak OBD sensor hooked up to it, and using Dr. Prius it is giving me code P3000P0AFA. When I first cracked open the HV battery compartment to inspect, I immediately noticed a lot of corrosion on the negative terminals especially. I removed all of the nuts and bus bars to clean them up. Used sulfuric acid on the copper bars, then vinegar, then 2500 grit sandpaper to shine up the contact side. Cleaned up the nuts with carb cleaner. Put everything back together, codes still came back. A typical battery monitor view is shown in one of the attachments. Block #1 is consistently low, so I figured one or both of those modules were bad. So I bought two new (reconditioned) modules. After replacing those modules, there was no change. The code came back after deleting and apparently had no change to the voltages it was reading. The modules I removed looked fine to me still. Nothing leaking, no bulging sides, no corrosion. Both read almost right at 8 volts across the terminals of each. Those don't seem like batteries that have a low voltage issue to me. I need some ideas of what to try next before I resort to taking it in to a shop. I'm suspecting that the battery is actually fine but it is something in how the ECU senses the voltage maybe that is the issue. Or maybe in the ECU itself, I'm not sure how issues with that manifest. I did pull out 3 of the ECU connectors and didn't see any corrosion or anything out of the ordinary, but I didn't look with a light and magnifier.

Some other symptoms that may or may not be noteworthy, the battery never really charges fully. The highest I have seen it get is 70%, but it typically goes between 55-63%. The other night I drove it into town in the rain for the first time and was running the defrost to keep the windows from fogging (not sure if either of those are significant to what happened next), then the battery level started dropping. It got all the way down to one bar which showed up as 30% when I got the scanner connected. I cancelled my errands and returned home, it charged back to a normal level when I let it sit and idle in my driveway for a while.

Okay, I'm open to suggestions and feedback. Thanks! I should mention I am not a mechanic, but I am a mechanical engineer who has spent most of his career designing automated machinery and a very hands-on and DIY guy, obviously.

 

Update: I inspected the connectors to the ECU and didn't see anything wrong. I figured maybe there was an issue with the wiring harness with some corrosion that I couldn't see. I replaced the harness and found the voltage sensing wire on the #1 block was broken where it crimps to the ring. I didn't notice it before as I was really just looking at corrosion. I connected everything back up, cleared the errors and they haven't come back. Everything seems to be working like it should now. Thanks for the advice! You were spot on!