[en] The structural and electronic properties of the Li_1+xV₃O₈ insertion electrode, where 0 ^≤ x < 0.4, have been explored by means of x-ray four-circle diffraction and through measurements of electrical resistivity, thermoelectric power, magnetization and electron paramagnetic resonance. Detailed structure refinements for x = 0.06 and 0.29 reveal the preferential and partial reduction of V ions which may give rise to low-dimensional electronic properties. The composition with x = 0 exhibits a quasi-one-dimensional polaronic transport in the localized states of band tails due to the slight deficiency of oxygen atoms. For x > 0.1 with nearly stoichiometric oxygen atoms, small polarons exist without carrier-creation energy at high temperatures, while at low temperatures the conduction may be of variable-range hopping (VRH) type. For x > 0.2, one-dimensional magnetic properties appear due to sizable exchange couplings and order-disorder effects of additional Li ions may lead to significant change of transport properties. For the intermediate composition 0 < x ^≤ 0.1, strong randomness of the Li doping and the congenital oxygen deficiency cause VRH states even at high temperatures