My 2OO8 Prius was purchased new in Fla, it has 84k original miles ==How long is the Warranty on the hybrid battery?
Florida is not a CARB state, so the hybrid system warranty should have been 96 months / 100,000 miles. I.e. already expired.
If in good repair otherwise and with only 84k on the clock I would put a new HV battery in it from Toyota. Consider asking for a good will discount from Toyota due to the low mileage. Worse they can say is no. But most likely the low mileage is the cause of the HV battery's failure. What DTC(s) do you have that suggest your HV battery has failed?