Need help determining HV test results

Hi all,

I have deep cycled (2-3 times) all my Prius HV modules and then have been taking readings over time to see the drop in voltage. Cut off was at 7500mAh.

Note that this HV pack was already opened and it seems that some modules have changed as the serial numbers are close but ordered differently.


It seems clear that module 6 and 25 need replacing, but there are 3 modules I am not too sure about. these are 9, 15 and 16.

All modules dropped about 0.06V to 0.08V after 1 min of 21W lamp connectionaside from Module 6 which dropped 0.12V. Module 6 was found at 6.51V when opening the HV battery, the other modules ranged in voltage from 7.48V (module 28), and 7.80V (modules 2, 8, 25)

On deep cycling, all modules reached the 7500mAh capacity aside from modules (15, 25, 28) module 11 too 6 deep cycling to reach 7500mAh.

Module 15 after 6 deep cycles had discharge and charge of 489 and 531mAh respectively, and reached a final voltage of 7.17V. After 10 days, it had dropped to 7.07V, so I deep cycled it again it dischared to 122mAh,and charged to 7500mAh and 8.35V. So I am not sure what is going on here. It would seem that the new charger EV-PEAK 4x100W was not functioning correctly.

I noted that on deep cycling the same module using the same cables, and just changing the port, I would have completely different charge discharge cycles... from 36mAh and 48mAh, to 4485 and 3921mAh after changing port. The low values always occurred with port 4, so I have sent out for a replacement unit.

After this discrepancy, I decided to charge all cells to full and see what the discharge rate would be over time. Charing to capacity took anywhere from 10 min to 170 min and all cells charged to 8.01V and 8.46V, with the exception of module 15, only charging to 7.17V. Discharge rates vary from 0.18V to 0.63V after 9 days of rest. These somewhat correlate to the original voltage - the higher the start voltage,the bigger the drop in voltage over the 9 days.

As things stand, I don't have a certain way of telling which cells are good, which are on their way out, and which need replacing now.

i have attached the file with results.

Any pointers would be greatly appreciated as I hope to get the car back on the road as soon as possible and not have to have this issue again in the near future.

Thanking you sincerely.

Roberto