Nexpower/Project Lithium Battery Issue - Blade #12 Failure?

Background:

• Bought the car in January 2023 with 218k miles. Pretty good condition overall. After testing, the traction battery was on its way out, so I looked into the ProjectLithium batteries. This is my first Prius, but I've learned a fair bit about them over the past two years.
• I installed a NexPower first batch V2 lithium battery in July of 2023. The car has been driving great since then.
• Occasionally the dash display fails to light up, but this usually resolves after a day. I believe this is related to the combination meter and unrelated to the present issue.
• On 8/7/24 I replaced the 12v auxiliary battery because I had deduced it was the cause of a recent no start, and an issue I had in January 2024. That battery was 6 years old.

The present issue:
On Friday 8/9, I drove to my work (10 miles, mostly highway 55mph) and it drove fine. When I left in the evening to go home I stopped by a friend's house briefly (about 1 mile from my work) and left the car on with the AC on while I talked with him. The engine never shut off during this 5-10 minute chat which seemed a little odd. I then left and began driving home. As I started accelerating after a stoplight the display beeped and said "Problem" and showed a red symbol, and the HV battery fan in the backseat shot on at high speed. The car drove but seemed to have no acceleration power, so I limped to a nearby gas station. I plugged in the code reader and checked Torque and it showed a 1.2v reading difference between module 12 and the others. The SOC also dropped randomly from 60% to 30%. I turned the car off, waited a minute, and then turned it back on and the issue remained. I switched it into drive and it could still move, but in limp mode. I moved it to the side of the parking lot and then parked it again. The module voltage difference had gone back down to a normal level (0.1-0.2 difference). I thought I would try clearing the code and see if it would let me get home. So I cleared the code and immediately the HV battery fan turned off and the car seemed to be acting normal. I test-drove it around the parking lot a bit and then decided to drive home. I thought it might just be a fluke because I recently replaced the 12v aux battery a few days before (although it had driven fine since I replaced that). I was able to drive all the way home fine (10 miles) and then as I turned onto my street I tested a quick stop and then hard acceleration. After the hard acceleration, the car threw the error, fan on, and lost all acceleration strength. The SOC dropped from about 55% to 30%, then after a moment began rising rapidly 1-1.5% a second until it reached 100%. I parked it and then switched to the Dr. Prius App and received the following reading. Note that Module #12 has double the delta voltage and resistance of the others.


The codes the system provided both times were: P0A80 and P3024.
At no point during either issue was the HV battery temperature outside of range.

Today, Sunday 8/11, after letting the car sit for a day and a half, I went out to run some more tests. When I turned it on it still had a fault code, but this time the code was P3022 and P3000. I cleared that and the car seemed to be idling normally as I watched the stat readouts with the Torque app. I then switched to the Dr. Prius app to see what those readings were.


Note that module #12 is showing yellow.



Once the car turned the engine off and stopped charging, #12 was still the highest voltage reading, and the delta voltage on it was also 1.70, compared to the others 0.53-0.59. A few seconds after this picture was taken, the car threw the error again (only P3022). I wanted to try a driving test, so I switched to monitoring it on my tablet for a larger screen. I cleared the codes, got everything connected and loaded up the Dr. Prius app and while I was still idling in park with the engine off, it threw the code again (only P3022) - turning the fan and engine on. The following picture from my tablet is directly after this.



All of the Sunday tests were taken while idling in my driveway. I never actually drove it anywhere. I haven't driven it anywhere since I got home Friday night.

I have contacted Jack at NexPower and now come here for suggestions and solutions. Are there any other tests I should try? Are these all symptoms of a bad #12 blade, or something else?

All help is greatly appreciated. Thank you in advance!

 

Thanks for the responses, everyone!

Today I took it apart and checked all the nuts. They were all tight and there was no corrosion anywhere except for a very minor amount on the main negative terminal wire, but not the contact portion. I inspected all of the blades and they all looked good - no signs of bulging, burning, corrosion, wear, etc. Unfortunately, I did not have my meter to check the voltage of the blades, so I'll do that another day.

Shoutout to @jacktheripper for superb customer service! He had a new Sodium V3 shipped out to me on Monday and I received it Friday - just 7 days after the blade 12 failure. I installed the pack and did a basic test drive and all systems seem to be working properly. I will do a more thorough test tomorrow.