We illustrate how to compute asymptotic interactions between discrete solitary waves of dispersive equations, using the approach proposed by Manton [N.S. Manton, Nucl. Phys. B 150 (1979) 397]. We also discuss the complications arising due to discreteness and showcase the application of the method in non-linear Schrödinger, as well as in Klein-Gordon lattices, finding excellent agreement with direct numerical computations.