2011 Prius Battery Reconditioning? - Sitting for 4 years

We actually run our Gen2-Gen4 Prius Dischargers down to 84 volts now. We were getting the occasional discharge beyond what the module could handle at 5 volts and we found that you could still increase the capacity by a significant amount though you are only going to 84 volts.

 

Discharging down to 84 volts is effective for batteries that are not very old and worn out.

I'm testing a single cycle method now. Charge-discharge-charge. I've noticed that after the first deep discharge cycle, the capacity increased significantly and the next 2 cycles did not bring any improvement, charging and discharging took the same time.

Years ago, I read an article made by someone who described how he completely discharged the entire battery pack to almost 0 volts and recommended to reсondition it that way. I ignored it at that time, because I knew how to do it “the right way”. When the RC chargers couldn't fix my two battery packs, I started researching how to do it a really right way.

I have heard different stories why you cannot discharge to such a low voltage, but there is no proof in favor of these stories.
However, I don't think battery packs less than 10 years old should be discharged to such a low voltage.

 

Hmm, that sounds like it would be worth looking into. Maybe when life slows down a bit for us.

So when testing the discharge cycles, how far down was the first deep cycle that showed the most capacity increased? Were the next 2 cycles at a lower voltage?

 

This depends on the condition of the battery.
For the past few years I have always discharged below 84 volts and have also tried discharging down to 5 volts in the first cycle and in 3 cycles. I usually discharge fresh batteries to 40-80 volts. Batteries with over 150k miles and over 10 years old i discharge down to 5 volts.
I have 3 batteries that I need to recondition on three low mileage Priuses: a 2007 with 68K miles, a 2012 with 102K miles, and a 2013 with 78K miles. I'm thinking about discharging the third generation batteries to 80V and seeing how much the capacity rises.
2007 battery I'm going to discharge below 20 volts. Although it only has 68k miles, it is 17 years old.

I've cycled this battery once down to 5.4 volts.
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I tested 2 modules which I checked before the cycling. The capacity is now 7100mAh, but this is not a good indicator, it should be around 8000mAh.

 

All you need to do with this battery is to discharge it as one unit with a low current of 300-500 mAh down to 80 volts and charge it with the same current to a maximum of 239-242 volts, depending on the condition of the battery.
I didn’t come up with this and it’s not Hybrid Automotive, but this is what scientists say who know what they are talking about and this is confirmed in practice. However, these people did not consider the option that someone would restore 15-year-old or older batteries.
RC chargers are not capable of discharging and charging with currents below 1A and they cannot balance all modules as one.

Read here what the nickel-based batteries reconditioning process is.
http://ni-cd.net/nicddownload/NA_Memory1.pdf

 

I have been using a CQ3 charger to recondition/test my modules. I learned that, according to Battery University,that a fully charged NiMH battery loses 20% capacity in the first 24 hours. So, to get the highest readings, retest immediately after a discharge/charge cycle. My modules have tested better than 5000 mah if I retest without delay. New modules will provide greater than 6500 mah, but I do not know under what conditions.

 

Even lithium Prius packs after being fully charged in the car discharge some after then charger is removed.
It's good to know what the specs are and it's even more helpful to have some history of the packs to compare results with. Unfortunately there are only so many ways of getting that history data to compare with reconditioning results. At least now you know that you're getting 5ah out of your C3Q charged modules at the point you tested, so you can compare with the next one, if / when that time comes.