We propose a self-consistent mean-field lattice-gas theory of intercalation compounds based on effective interactions between interstitials in the presence of the host atoms. In addition to short-range screened Coulomb repulsions, usually discussed in the lattice gas models, the present theory takes into account long-range effective attractions between intercalants due to elasticity of the host matrix. The mean-field phase diagram in the space of interaction parameters contains the domains of first- and second-order transitions of the order-disorder type, separated by a tricritical line, and the domain of the first-order transition of the gas-liquid-type separated from the homogeneous state by a critical line. Theoretical predictions are shown to be in qualitative agreement with the grand canonical Monte Carlo simulations. The peculiarities of the phase diagram give an insight into different types of behavior of the open circuit voltage observed in rechargeable batteries, in which an intercalation compound is used as an electrode material.