A detailed theoretical study of proton transfer reaction in protonated imidazole, 1,2,3-triazole, and tetrazole dimers, the basic components of polymeric membrane used in proton exchange membranes fuel cells, has been carried out. In particular, several approaches based on density functional theory have been considered and their results compared with those provided by post-HF methods. From a computational point of view, these molecules appear to be a very challenging playground also for robust and recent functionals. Indeed none of the considered approaches provide results in close agreement with the reference post-HF data and a combined BMK//B3LYP model seems the only approach able to reproduce both the energetic and the structural features. From a chemical point of view, two new mechanisms of proton transfer in tetrazole dimers have been investigated and found to be more favorable than that previously hypothesized in literature. At the same time, the theoretical results show a direct connection between the obtained proton transfer barrier and the charge localized on the transferred hydrogen.