A controller for a rechargeable battery that improves the recovering
efficiency of the energy used to charge the rechargeable battery and
prevents the life of the rechargeable battery from being shortened by
overcharging. The controller includes a voltage measurement unit for
measuring terminal voltage of the rechargeable battery and a control unit
for setting a plurality of input maximum voltages, each indicating an
upper limit for charging power input to the rechargeable battery during a
predetermined time. The control unit sets a plurality of reference
voltages respectively corresponding to the plurality of input maximum
values. When the terminal voltage of the rechargeable battery increases
to one of the reference voltages, the control unit lowers the input
maximum value corresponding to that reference voltage.