Issues with HV Battery install

I have 2002 Prius with about 140K miles. The triangle warning light came on multiple times in previous months and the car finally cut out in early July. It threw codes P3000 and P3009 and the dealer isolated the problem to the hybrid battery. They wanted $2700 for a new HV battery install so I looked for other options.

After that, I removed the HV battery from the car and the invidual cells all tested >7.5V with a multi-meter. I took the battery up to a specialty hybrid battery repair guy in Chicago and this was his diagnosis:

There was extensive corrosion build up on the terminals and bus bars, and we noticed some unusual arc flash damage on each end of the battery. The corrosion may have provided a path between the two sides and allowed the arc flash to happen. We have never seen this arc flash damage inside one of these batteries before so we were not sure what to expect. If you open the battery when you get it back you can still see some black residue on the battery and the underside of the cover on opposite corners (driver front and passenger rear corners).

So we disassembled everything, cleaned the terminals, replaced the bus bars, put it back together and reconditioned the whole pack. We then put it into our 2001 Prius test car and it worked fine on the test drive, no codes or lights or issues at all...
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Sounds like good news right? So today I put the battery pack back in my car, hooked up all the cables again, and re-inserted the orange fuse. Then I removed the negative terminal of the 12V battery for a few minutes to clear codes and replaced the terminal. The car started up with no problem but after about 5-10 sec, the triangle light and check engine light came on again. After another 5-10 sec, all the warning lights come on and the car stalled. I have checked connections and cables multiple times and I am almost sure everything is together as it was before. I have had the same result several times.

Any suggestions what I can try next? As you can probably tell, I am a novice at car repair and especially hybrid battery car repair.

Thanks.

 

The dealer read the codes when it took it in last month. I do not have a code reader unfortunately.