I'd possibly believe it for virgin batteries, but how about recycled ones.
Every recycled battery was once a virgin and has created horriric damage in Sudbruy. This deserves extra scrutiny only because the Prius is touted as the greenest contraption on 4 wheels out there. Each of the 4 processing steps in different countries add further pollution making the Prius a lot more black and brown than most people think.
NiMH battery recycling only involves recycling the nickel, which is the most expensive component in the battery.