A schedule recording section (4) records a user's schedule. A SOC (state-of-charge)
optimization planning section (5) plans the SOC of a rechargeable battery
(21) based on the user's schedule. The planned control target SOC is optimized
through a comparison between the continuous charging characteristic of the rechargeable
battery (21) and the length of an operable period or the amount of electric
power to be secured at the time of battery-powered operation. For example, a control
target SOC is set at a full charge in the proximity of the period during which
a battery-powered operation time is expected to be long. A control target SOC is
set lower enough than a full charge in the period during which a connection to
an external power supply (A) by the AC adapter (11) is expected to continue
for a long time. A power-supply control section (3) controls the charge
and discharge of the rechargeable battery (21) according to a plan for the
optimization of the SOC.
