Charging of Electric Vehicles (EVs) from roadside charging points (CPs) constitute as unique transaction events. These events can be verified by and stored over a distributed blockchain, where the CPs themselves act as miners. Mining being resource intensive, the CPs are expected to remain fairly loaded due to dense EV charging. We thus propose to reduce relevant mining overheads for such a blockchain over smart EV-utility grid using geographic segmentation of the miner set. Depending on the physical locations of CPs and their connectivity graph, we divide an initially unsegmented mining cluster into several smaller clusters geographically, where each cluster verifies only their local transactions. This reduces mining parameters per-transaction and per-block, while achieving parallel block generation across segments. We argue that for transactions like EV charging that are coupled to their geographic source locations, it is sufficient to have smaller independent, but parallel mining segments. We prove that reducing the mining segment size does not necessarily compromise blockchain security. We corroborate our claims through experimental results, where we achieve an average improvement of 48% with respect to CPU cycles expended and mining energy consumed per block and 45% with respect to mining time per block with half-sized segments as compared to an unsegmented miner set. Our results further prove that the proposed segmentation outperforms other geographic clustering (e.g. K-Means clustering) for blockchain applications. Owing to parallel block generation, the mining energy required per block is reduced from 19 J to about 0.02 J over the same grid.