My experience with Hybrid Battery repair/replacement

After about a year of owning a used 2012 Prius with just over 200,000 miles, the dreaded "triangle of death" light appeared on my way home from work. I managed to get the car home and immediately jumped on the internet to search for a solution. I found a reset method: disconnect the hybrid cable, wait about 10 minutes, and reconnect it. Success! The light disappeared, and I was a happy driver again.

Exactly a week later, almost in the same spot on my way home, the ominous triangle lit up again. I repeated the reset process, and once more, the light went out. The following week, the same thing happened in almost the exact same way. While these resets were buying me time, I was researching and gathering the necessary parts to complete the best repair option I had decided on.

Out of all the several youtube videos I watched, I decided to start with the one posted by Gregg Festo:
Hybrid Battery Pack Refurbish - Step-By-Step w/ Settings - 2nd & 3rd Gen Toyota Prius - CQ3 Charger

I liked his video because he provided detailed information about the required charger and all the necessary settings, along with step-by-step instructions for testing the battery modules. When the big day finally arrived, I removed the battery and began testing it using the CQ3 charger I had purchased from AliExpress (at half the price compared to Amazon).

I had designed a neat spreadsheet on my laptop and followed Greg's instructions carefully. The results were disappointing—none of the modules discharged or recharged to 5000mAh. In fact, all of them were below 1000mAh. I thought at least some modules would reach 5000mAh by the third cycle. It didn’t make sense that all the modules could have gone bad at the same time.

Frustrated, I started googling again and came across this page:
PROLONG® Battery Discharger User Guide

The page—and the website overall—offers a wealth of information. Somewhere on the site (I can’t locate it now), I found a note explaining that NiMH batteries are durable enough to be discharged to 0V. Armed with this information, I discharged the cells to 4.6V, 3V, and 0V in different cycles.
After these cycles, about 11 of the cells bounced back to 5000mAh, just as Greg described. However, 12 cells didn’t recover at all, while the remaining cells stabilized between 2000mAh and 3000mAh. To address this, I replaced the 12 bad cells with used ones I purchased from eBay.

The next step before reassembling the battery was balancing, and I followed Jose’s video for guidance (linked below):
Easy method to balance the Toyota hybrid battery (NiMH)

By the way, Jose's channel, Hybrid Solution Diagnoses, has a lot of great videos.

For the balancing process, I picked up two aluminum rods from Home Depot and repurposed a broken wooden drawer I had in my garage. I laid the rods across the drawer, arranged the modules in parallel, and left them to balance for 48 hours.

Before coupling the battery and reinstalling it in the car, I cleaned the bus bars, following another one of Jose’s videos as a guide:
How to clean the bus bars for toyota hybrid battery service and maintenance

Using the Dr. Prius app, I checked the battery's life expectancy, which improved to 67% compared to 36% before replacing the modules. The hybrid warning light disappeared, and the car drove well.

However, six weeks after the module replacement, the dreaded "triangle of death" resurfaced!

Over the next few weeks, I went through the same process, replacing a few modules each time I pulled the battery. After each replacement, I was able to drive the car for a few weeks, but the light would return within six weeks. Eventually, I had replaced 18 modules when the dreaded light came back again.

Using the Dr. Prius app, I noticed a module that was charging and discharging faster than the others. I pulled the battery and ran the two cells in that module through three cycles of discharge and charge, following Greg’s instructions. During the process, I observed that one cell completed all the cycles in just 10 minutes, while the other was still on the first cycle. I replaced the cell that completed the cycles too quickly.

Six months and over 7,000 miles later, I was still driving the car without any battery issues. Then, one day, the "triangle of death" appeared again. This time, the Dr. Prius app helped me identify another module that was consistently low. I replaced the cells in that module, and 10,000 miles later, I’m still enjoying the car trouble-free.

Lessons and Suggestions

1. Complete Battery Replacement is Best
   The most reliable solution for the "triangle of death" is a complete replacement of the hybrid battery.
   
   
2. Reconditioning Facts
   Based on my research and YouTube videos, a completely dead battery cannot be reconditioned. Reconditioning can only prolong the life of a new or partially functional battery. For example, I still have 10 cells from the original battery that are working in my pack.
   
   
3. Temperature and Battery Wear
   The "valley description" of the battery is accurate. Modules in the middle of the pack fail first due to higher temperatures, while the ones at the ends last longer.
   
   
4. Selective Module Replacement
   If you choose to replace bad modules instead of the entire pack, don’t cut corners. For batteries 10 years or older, keep the five cells at both ends of the pack and replace all the cells in between. This approach saves significant time and effort.
   
   
5. Weakest Cell Rule
   Your battery is only as strong as its weakest cell. A single cell that charges or discharges too quickly will eventually trigger the "triangle of death."
   
   
6. Dr. Prius App Insights
   If the Delta Voltage in the Dr. Prius app shows anything other than zero, the "triangle of death" is imminent.
   
   
7. Bus Bar Replacement
   Don’t waste time cleaning the bus bars—buy new ones instead. While Jose’s cleaning method works, it’s tedious and time-consuming.
   
   
8. Prolong Battery Charger
   If your budget allows, invest in a Prolong battery charger. It will save you a lot of time and effort.
   
   
9. Stay Organized
   When pulling the battery, stay organized. Use zip-lock bags and Post-it notes to store screws and label each piece you remove.
   
   
10. Balancing Precautions
    If you’re using Jose’s method to balance cells, pay close attention to polarity. I accidentally placed one cell incorrectly, causing a big spark and burning the aluminum rod.
    
    
11. Used Cells from eBay
    Be cautious when buying used cells from eBay. Some may fail—it happened to me!

I hope this helps someone out there!

 

Ah! Thanks for pointing that out. I totally missed including three vital info:

1.) Error code: P0A80
2.) Along with the triangle of death light, I also got the hybrid error msg: Check Hybrid System. Stop vehicle in a safe place.
3.) The car kept running on the combustion engine and wouldn’t switch to electric mode while the message and light were on

On balancing, I manually trickled charged each module to the fullest before using Jose’s method the first time I pulled the battery pack. Subsequent pullings, I skipped the trickled charging portion and still the delta number on Dr Prius app disappeared afterwards.

The experience I shared here happened a little over a year ago and I relied totally on my memory when I wrote the piece. I should have taken time to gather the info in my notes and spreadsheet.

I also realized I mixed up the terms (cell, module and unit) in my post. Dr Prius uses unit for two modules. You have provided the correct
Cell, module and battery info in your response.


Thanks again for taking the time to respond. If I had to do this again, I’ll use a suitable Prolong product.