If you buy a "high capacity" battery and can still use the standard battery cover, then it ISN'T a high cap battery. Longer battery life (with current technology) requires a larger battery, thicker basically and WILL require a larger, modifiied battery cover. The original one with your 7100 will NOT fit. www.shopblackberry.com
wll be carrying the High Cap battery, but are currently waiting for the matching, larger battery cover to go with it. It will be sold in a combo pack, battery plus new cover, for the various models of the 7100.
ACC-07496-001 Extended battery with larger cover for 7100t or 7100r
ACC-07673-001 Extended battery with larger cover for 7100v
More in development.