If I remember correctly Warranty Direct would cover the batteries But if I'm wrong I wouldn't personally be bothered after seeing a video on youtube about a company in America supplying new replacement battery cells for the Prius. I think by the time the batteries in my car needing attention then that same company, of which I believe there are quite a number spread about America and by that time too they'd be here in blighty, I'd get replace cells and change them myself.
Toyota will do my servicing. Lexus will do the hybrid heath check and all other electrical mechanical items will be covered by WD.
It' my choice at the end of the day and also my car will undoubtedly be the most looked after is300h out there and for a fraction of the cost the 'I saw you coming' company known as lexus.
Thankyou