Lattice structures, due to their high, tunable specific strength, stiffness and energy absorption, are increasingly gathering interest for development towards lightweight aerospace structures. Additive Manufacturing (AM) has enabled the fabrication of complex lattice materials with a wide range of relevant mechanical properties. However, these lattice materials feature AM induced manufacturing defects, particularly geometric defects including surface roughness, strut thickness variation and strut warping, that can strongly influence their mechanical properties, particularly their effective stiffness, strength, and elongation to fracture. This makes it difficult to predict the mechanical properties of a given lattice design without mechancial testing, thus increasing the number of tests needed to validate lattice design space exploration, slowing lattice optimisation studies. To address this aspect, this work investigated of Body-Centred Cubic (BCC) lattices with explicitly-represented AM defects to predict the influence of these defects on the effective strength, stiffness, and post-peak mechanical behaviour of the AM lattices through finite element (FE) modelling. FE analysis of lattices without defects and with varying degrees and distributions of strut waviness, were performed. This showed the quantitative impact of these geometric defects on the residual mechanical properties of the lattice. It was found that randomly orientated strut warping had only a minor impact on the stress-strain properties of these lattices under compression. However, if the struts were warped in a symmetric pattern, the strut warping altered the energy absorption under quasi-static compression, while having a minimal impact on the effective stiffness and strength. This suggested that strut warping could be intentionally utilised to produce BCC lattices with tuned energy absorption. This study contributes to methods for the design and mechanical assessment of truss lattices.