Htc is releasing extended battery covers & extended batteries (1340mah & 1800mah) for the GSM Diamond and Pro. I doubt these will even fit the CDMA versions due to any minor design changes on where the covers snap in but one can hope right?
http://www.htcaccessorystore.com/uk/....aspx?i=166204 (Diamond Extended Battery & Cover)
http://www.htcaccessorystore.com/uk/....aspx?i=172018 (Pro Extended Battery & Cover)