A battery unit may comprise a first cell type and a second cell type electrically connected at least in series, wherein the first cell type may include N first cells, the second cell type may include M second cells, and N and M are positive integers; the first cell may have a discharge cell balance rate of CB1, the second cell may have a discharge cell balance rate of CB2, with 0.5≤CB1≤CB2≤1.4, and when the battery unit is charged to 95%-100% of the state of charge, the first cell may have a corresponding open-circuit voltage change rate of not greater than 0.005 V/% SOC, and the second cell type may have a corresponding open-circuit voltage change rate greater than that of the first cell.