Need advice with HV battery computer

Hello. I'm a new member of the forums here but I've been reading posts for literally days to get troubleshooting info. It's been a great help as I just recently had a problem that I couldn't figure out. I finally did figure it out but now I need some advice as how to proceed.

So here's the scenario. About a month ago I bought a 2009 Prius (gen-2) with ~189k miles on it. It was a single-owner car and had all the maintenance records going back to the sale date. It was in great condition but it never had the traction battery replaced/reconditioned. Zero issues with anything else (no leaks, didn't burn oil, etc). BTW, I work on our cars and I'm also an electronics engineer. That being said, I knew it was just a matter of time before I would have to address the battery. And, at the time, I thought I had an idea of what to look for when the batteries were on the way out.
So, day before yesterday my wife and I jumped in the car for a grocery run. Our driveway is about 300 ft long. As I was pulling on to the road, we head a loud smack... which we both were confident that it sounded like something hit the roof! I immediately pulled over, hit "P", got out and walked around the car but didn't see anything. We live in a heavily wooded area and we are no strangers to the sound of hickory nuts hitting car roofs.
So I got back into the car and immediately noticed that all the warning lights were on and even the MFU screen had an icon of a red car with "!" on it! Of course my reaction was Wth?! I mean, I was out of the car for just a few seconds... what happened? Maybe in my haste I actually didn't press the park button? Anyway these were my thoughts at the time. So I powered the car off, waited a few seconds, and powered back on as normally. But all the lights remained! And it would not go into any gear except neutral. And the "B" breaking gear was gone from the heads up. So that's when I started researching and learned that this could be a symptom of a failing 12v battery. I found out how to get into the diagnosis menu and the battery was a little low. So I swapped it with a brand new one...the old one was the original factory installed unit. But all the lights remained. No READY, no start, no ICE.
Got my code reader out and had only one code: P0AFA, low hybrid battery voltage. This was odd because the MFU showed it was about 60% charged. Anyway, I cleared the code, but it would immediately return. And the car still wouldn't go. More research.

The day before this happened we had about 6 inches of rain in an hour. I read several posts about water leaks from the hatchback. And I did have a little water in the 12v compartment. BTW, there are little rubber plugs at the bottom of both (lt & rt) "cubby holes" to allow them to drain. With some of what I came across in the forums, I wondered if water had gotten around the traction battery & cables. I decided to jump in and check. Removing all that trim wouldn't have been so bad if it weren't over 90 degrees with 90 % humidity!
Once I got everything peeled back, and removed the access cover over the ECU, I found everything to be very clean and dry. There was no corrosion or rust on anything. Then I started pulling plugs from the ECU. The big white one had some carbon on the outside of the plug, but it was clean inside and all pins were shiny. The small white one had no issues. The orange one looked fine from the outside (before I unplugged it). I knew this was the HV sensor and from photos posted on this site and others, I couldn't believe mine would be bad, it looked that good. Until I unplugged it...
Attached photos.
So, I had found the reason why I was getting P0AFA's that wouldn't clear. Then I decided to take out the ECU and open it up. My first reaction was "This doesn't look so bad... can't see any actual components burned, just a little carbon dust...", until I lifted the circuit board and turned it over. Then my reaction was something along the lines of "Holy $&*@#!!!". Photos attached.
Ok. Now I need some advice. What would have caused this level of distruction? If I get another good ECU, what is the likelihood of it being blown to smithereens as soon as I plug it up? I'm pretty sure that my battery may need new cells/rebuild/reconditioning. I ordered a good wireless scan tool so I can get an idea of which cells are failing. But I need the ECU in order to do this. So I'm a little stuck. I don't want to get another ECU only to instantly blow it away. But if I knew the battery was so fubar that it would blow it up, then I'd strip down the module and check voltage on each cell manually. I intend to at least check out the condition of the bus bars, etc anyway. But I would like to know if anyone has experience with this to let me know if I'm just going to blow an ECU if I put another one in now.

 

Thinking about this a little more, I know that high voltage is across several pins of this connector. Since the case is not really sealed, I wonder what the likelihood is of some small insect to get into the case. I can see how something like that could be walking around in there and suddenly bridge some pins. Obviously, in my case, any evidence of this would have been vaporized. But just wondering if anyone else has seen it.

 

Cool. So it should be fine to get a replacement ECU and plug it up so I can at least pull status of cells? I figured I've already done the work to get to traction battery, I might as well do a referb job and clean all of the contacts/bus. I'm sure at least one blade is probably getting weak, but I need the ECU in line to get that info.

 

I'm very familiar with what could happen with high voltage DC. Used to work at a factory as their electronics maintenance engineer where most of the equipment was 480V. I've seen plenty of motor controllers that fried from arcing. It was a plastics company, so a lot of plastic dust around the business ends of production lines. Controllers that weren't sealed + dust + high DC... you get the idea.

Anyway, thanks for the swift replies! I didn't think it would be a problem to slap another ECU in there to do testing, but since this is my first hybrid and I couldn't find good info, I wanted to be sure one way or the other! Regardless of what the scanner actually says, I'll be manually testing each module anyway.

I may just take you up on your offer on the new wire frame. Shoot me an email.

Thanks!

BTW, that's a 89890-47092.

I know there are a few different part numbers for these ECU's. I would normally look for another part with the same #, but I've seen a few things out there indicating that maybe a couple of other numbers may be used in certain models. I'd have to guess higher numbers might have added features/options or some revisions. But I'm only guessing. So, are other models compatible (for 2g's anyway)?