We derive an energy bound for inertial Hegselmann-Krause (HK) systems, which are a variant of the classic HK model that allows agents to change weights as they please at each step. We use the bound to prove the convergence of HK systems with static agents, which settles a widely believed conjecture. This paper also introduces anchored HK systems and show their equivalence to the symmetric heterogeneous model. Index Terms-Hegselmann-Krause (HK), model organism.