3rd Battery Reconditioning

My 2008 Prius threw the triangle of death last week. I watched the banks using the Dr Prius app and noticed bank 2 would sometimes work correctly and then a few minutes later would drop low in volts causing the voltage differential to rise up over 1.5 volts. I've had battery problems twice before and removed the pack myself, reconditioned the cells replacing the bad/low cells with better used ones from Ebay. I discharge to 6.3v at 1.5 amp and charge at 5 amp.

The car has almost 300k miles and I'm thinking the cells are getting past their useful life, but I just don't want to spend the $2k or more to get a new or reconditioned pack. So my plan is to keep reconditioning myself and hopefully get 12-18 months between failures.

One thing I've never understood is how to match cells together into banks. My previous approach was to place the highest mAh battery with the lowest, the second highest with the second lowest, etc. Can anyone help be with the best approach to building the banks, and also when do you determine if a cell is no longer useable? I've been getting rid of any cell below 5000 mAh, but again don't know if that's the best approach.

Any help appreciated.

 

I could really use some help on this thread if anyone would be willing to give me some advice! Just to update my current reconditioning efforts I'm finding my cells have really lost some capacity since the previous repair. Most cells are topping out in the 4000's and 5000's mAh range, and at least 8 of the cells are only 1000 to 3000. I have 10 extra spares over 5000, so hopefully I'll be able to build the pack using batteries above 5000. Just need some advice on how to build the pack, should I use capacity or volts or some other means to pair the cells??

 

Thanks for the reply! The first repair lasted about 2 years, the second maybe 1 1/2 years. I'm not driving the Prius much this last year since I bought a new all electric car, so it sits for weeks at a time. But I'd like to keep the Prius as a 2nd car. I read on a battery sellers website that to maintain their warranty you should drive it for at least 30 minutes once a month, so will try that to help. On another note I also noticed lots of corrosion on my copper plates. I had cleaned them last time with salt & vinegar, but read somewhere I should also polish them with fine steel wool which I'm doing now. Saw they sell the plated copper plates on Amazon, not sure if that's worth the $40 cost or not.

 

Did a little more digging and found my time-frames were off. I did my first reconditioning in June 2019, then the second in October 2019, only 4-5 months. But since then it went almost 4 years without failing. Not sure anyone's interested but here is the status of where I'm at with building my new banks.

After charging & discharging each module 3 times, I've decided not to use my previous method of highest mAh cell with lowest mAh cell. My RC charger showed the final voltage after each charge, so I recorded that. I then matched the highest charge volt cell with the lowest charge volt cell, etc, and found the voltage differential between the banks was only .10v. When I had charted the previous highest-lowest mAh cell method the differential was .30v. With this new method my highest mAh bank is 13,266 and lowest is 10,488, but since it's the voltage differential that triggers the red triangle of death I figured this method might work better. Time will tell.

On another note not sure why only one person was willing to offer some assistance, but thought putting this out there might be helpful for others. Also I think it would be nice for this chat forum to have a hybrid battery specific section, and I'd also think it would be nice if there was a place for sticky notes for experts to place help threads that folks could use in addition to searching words.

 

Thanks, appreciate the recommendation & feedback.