Hybrid battery reconditioning data/results, 2005 Prius

Wanted to share some data and observations about hybrid battery reconditioning and how a failing battery can be brought back to life without replacing any parts. Lets start with a 230k mile 2nd gen Prius battery, 171G to be exact (January 1st, 2005). The battery was often charging into the green and quickly discharging down to 2 bars for weeks prior, finally the red triangle came on with a code P0A80. Within a few days of failure the battery was brought to be rebuilt. The battery computer and harness are in good shape, no corrosion.



First graph shows each module discharged to 6 volts @ 5 amps, followed by a 2 minute rest period and another discharge to 6v @ 0.65 amps. The battery is only as strong as the weakest module, from this graph we can see that the car had very little capacity available. The strongest module was sitting at almost 5ah, while the weakest 3 were at less than 1.4ah. A 2nd gen Prius typically discharges the battery down to 2 bars, or approximately 14.5v per block, the actual remaining usable capacity was not even 0.5ah. Well, what if we're looking at a battery that was pulled at 2 bars? The maximum possible charge is limited by the strongest module which would delta -v and hopefully the battery computer would catch this and terminate the charge, assume full SOC and display all green bars on the MFD.




This graph shows a simple re-balancing of the battery, full charge to delta -t followed by a discharge to 6v. To measure actual capacity of each module. Our best modules show nearly 6ah capacity while the weakest modules are less than 4ah. This step alone could potentially extend the battery life by months or even a year but we aren't done.



This is the weakest module of the bunch, number 16, located in block 8. After 6 full charge/discharge cycles the capacity improved from 3.8ah to 5.75ah. Noticeable improvement were seen between the 5th and 6th cycle, additional cycles may be beneficial.



Each peak represents a charge termination point. The first 3 full charge cycles were limited by the temperature rise of the module, after repeated cycles this internal resistance of the module decreased leading to improved thermals. Even though the temperature of the room was 15 degrees higher than the start of the 1st cycle and module was heat soaked it hit lower temperature on the 6th cycle (7.5ah) than it did on the 1st cycle (5.2ah).


This is the strongest module, module #1, block 1. Power under the curve improved but very little overall capacity increase. The sweet spot appears to be 5 to 8 cycles, weaker modules positioned towards the middle require more cycles while the outside modules show minimal improvement past the 3rd cycle.



After 6 full charge cycles the capacity, performance and temperature rise of the battery improved dramatically. I felt like it had more to give.



I was running this over the weekend so I squeezed in another 4 cycles for a total of 10. This is the final result, all modules reached 6ah or above.


If a battery issue is addressed early enough performance can be restored and battery life extended without replacing any parts. Even if the battery hasn't failed but performance has degraded reconditioning can restore performance and extend battery life. I have more results on other Toyota hybrid such as Prius C, 3rd gen, 4th gen and Camry hybrid if there is interest.