The disclosure relates to a battery lower casing and a battery system. The battery lower casing comprises: a support frame comprising a plurality of fixing beams that are connected end to end to form an accommodating space, wherein each of two fixing beams opposite to each other comprises a fixing portion extending toward the accommodating space, each of the fixing beams comprises fixing tabs at a side of the fixing beam away from the accommodating space, and the battery lower casing is connected to a target object through the fixing tabs; and a bottom plate connected to the fixing beams.