C1259 and red triangle after hybrid battery rebuilt and ECM sent out for repair

I recently pulled and tested my HV battery pack out of my 2002 Prius and found a single cell that needed to be replaced. After returning the battery pack to the car, I began to get random misfire codes(P3000) so I had a friend check it out. He thought that maybe the ECU was the culprit, so I sought out a solution on Ebay. There is a Seller offering to repair your ECU for $80. You ship it to him, he diagnoses the ECU and repairs it and returns it in a timely fashion. I won't name the Seller because I personally had a bad experience. He contacted me maybe two weeks after receiving my ECU and told me over the phone that he could not determine if my ECU was bad or not, but he could sell me a reconditioned one, already programmed for $400. It felt like a bait & switch so I refused the offer over the phone. He agreed to return my ECU to me and refund the $80...and he did return my ECU, but kept the $80. I was not aware, but apparently he was that if a transaction falls outside of the allotted time Ebay won't investigate fraudulent returns. He basically held on to my ECU until Ebay refused to look into it. My credit card company is investigating the bogus return.

So far, I'm out of the $80 but my ECU finally arrived back to me. I re-installed it into my car and now all I get is the following code:

C1259 TOYOTA - HV System Regenerative Malfunction

The red triangle frequently appears so I'm hoping that replacing the ECU will do the trick. Any recommendations on a trustworthy place to purchase one? What exactly is involved with making it compatible with my vehicle? I'm open to a salvage yard unit, but not if it will just cause me more problems.

 

I'm reading the codes from an Actron CP9580A Enhanced AutoScanner Plus scan tool. I'll read them from my Techstream software once my laptop becomes available, but until then, I'll research whether my Actron can do the job properly.

So if I'm clearing the codes with my Actron and red triangle is disappearing it's really not clearing? It comes back soon after I clear it. I assumed the issue was triggering it.

 

Sorry, just a typo. The code is P0300.

 

I finally got my laptop updated and I was able to run the Techstream diagnostic software. I found a P3000 & a P3009. They both had “History” status. I cleared them and so far the car has been running like a dream. I’ve only put about 20 miles on her so I’ll continue to drive her until the OBDII status shows that I can get it inspected. I hope this solves the issue. I miss putting 80 miles a day commuting back and forth to work for like $12 a week. I’ll be back should anything else arise. Thanks a bunch!