Battery charger (10) may include a power source circuit (22) for charging rechargeable batteries (58) when a battery pack (50) is connected directly to the battery charger or is connected thereto with an adapter (30) interposed therebetween. The adapter may include a discharging circuit (42) for discharging the rechargeable batteries. The adapter may also include a switch (48) for alternatively connecting the rechargeable batteries with the discharging circuit or the charging circuit of the battery charger. The battery pack may have a memory (61) storing a flag indicating whether a refresh process is required. The adapter may further include a control portion (41) for controlling the switch. When the battery pack has been connected to the battery charger via the adapter, the control portion may preferably controls the switch on the basis of the flag stored in the memory of the battery pack.