The potential variation, charge transfer and lattice distortion across grain boundaries in polycrystalline superconductors play a crucial role in the transport properties of the material. in particular, the grain interfaces often act as weak links to the superconducting current, which limits the critical current densities that may be obtained. in the case of the high Tc superconductor Bi2Sr2CaCu2O8 (Bi-2212), special interest is paid to (001) twist boundaries since, in part, they are dominant in c-axis aligned tapes and wires, but more interestingly because the superconducting critical current is found to be independent of twist angle for this system. Such grain boundary behavior is presently not understood, and is further puzzling since “impurity phases” of Bi-2223 or Bi-2201 (consisting of additional or missing Cu-Ca-0 planes, respectively) are commonly observed at the (001) twist boundaries. with the rich structure found at these types if interfaces, understanding the potential distribution may lead to new insight about the boundary properties.