How many miles are on the car? When my mileage dropped like that I replaced all the cells in the HV battery and when I tested my old ones I found 8-10 cells going bad. It only cost around $1,400 and that is WITH buying the Autoenginuity Diagnistic PC software and hardware for Toyota. You can get new cells from wrecked low mileage cars from 04-09. Newer car battery cells may work but I have not heard of anyone using them.