Group key management protocols are crucial in establishing secured communication channels for collaborative IoT-based groups. The Internet of Things (IoT) dimension includes additional challenges. In fact, resource constrained members within dynamic and heterogeneous groups are unable to run existing group key protocols. Furthermore, these protocols need to be scalable and fault tolerant to suit growing and sensitive groups. To face these issues, we enhance our previously proposed protocol called Decentralized Batch-based Group Key protocol (DBGK). Using polynomial computation to secure data exchanges, we considerably improve its scalability, fault tolerance and collusion freeness properties. This gain is achieved thanks to the ability to include additional unconstrained members (controllers) while inducing a very limited cost on the constrained members. Furthermore, we include an energy preserving blockchain-based mechanism to authenticate group members credentials in a distributed manner. To assess our new protocol called DiStributed Batch-based Group Key protocol (DsBGK), we performed a detailed theoretical security analysis to evaluate its behaviour against well studied attacks in the literature. Furthermore, we validated this analysis using a formal validation tool. To evaluate DsBGK performances , we performed extensive simulations. We proceeded by comparing DsBGK in term of energy cost, first, with DBGK, then with other analogous protocols from the literature. The results confirmed the security soundness of DsBGK, in addition to an improved energy efficiency compared to its peers.