According to a first aspect, a portable electronic device has at least two load circuits which are independently powered by different batteries. According to a second aspect, the load circuits are powered by the same battery, but their power lines are branched from a node located close to the battery, thereby reducing common impedance. According to a third aspect, two power lines are coupled through switches to two independent batteries, and are mutually coupled through a third switch. The switches are controlled according to the discharge states of the batteries. According to a fourth aspect, a battery charger charges two or more batteries by supplying current to them for short intervals in turn, so that all batteries reach full charge at substantially the same time.