An electronic apparatus which detects when a battery having a different characteristic is mixed in a plurality of batteries accommodated therein. An average voltage V1 per battery of plural batteries connected in series and an average voltage V2 per battery at a connecting point halfway of those connected batteries are detected. A difference in voltage |V1-V2| between the average voltage V1 and average voltage V2 is compared with a tolerable voltage difference .DELTA.V. If it is determined that a battery having a different characteristic is mixed, the operation of the apparatus is interrupted and an alarm is displayed or the supply of power is shut down.