My battery replacement journey

I recently replaced the High Voltage (HV) Battery in my 2006 Prius. I thought I'd put my experience here so it might help someone else in the same situation that I was in.

My Prius has 286,000KM (c.177,000 miles). Driving along one day and the Triangle of Doom, brake and VSC lights came on. It drove poorly after that.

I got a Nexas bluetooth code reader and the Dr Prius app. One module had failed. There was only one battery replacement service in Ireland that I could find and despite repeated contact, they never got back to me.
Garages here weren't keen to do the work and mostly directed me to Toyota. So I decided to attempt the battery swap myself.

I found a battery in a breakers (scrap yard). It came out of a 2007 car with 90,000 miles. It had been scrapped for front end damage from a collision. It cost me €400.
Using Chrisfix's video and some old Car Mechanics magazine where they did a Prius project as I guide, I got started. The strip out and install was straightforward. The new battery was in and the car was driving nicely again.

100km later I was greeted with the same warning lights and even worse performance. The car was refusing to change gear and just about limped back into the driveway. At this point I left the car for a week I was so frustrated with it.

A week later, I read the codes and they were different this time (P0A1D, P3000P0AC0, P0AFA, HV battery ECU fault). I opened up the battery pack and removed the battery ECU. The connections were heavily corroded and a pin or two were missing. Disaster! That's the risk of buying used parts.
Luckily I still had the old battery. I swapped the ECUs over and hoped for the best.

The car came back to life and has been driving perfectly for more than 100km.

Hopefully this helps somebody in the same situation as me.