Specific practices of battery replacement for an electronic device during power on comprise that: a sequence is from 1 to 2 to 3 when B is changed into A and the sequence is from 3 to 2 to 1 when A is changed into B; and a battery shortage of power is taken down and a spare battery with sufficient power is installed. The electronic devices such as a computer, a television and the like can be used movably like a cell phone as long as enough spare batteries are provided; expensive batteries with larger capacitance are not required because the battery can be replaced during power on; and the batteries with smaller size, lighter weight and lower manufacturing cost can be chosen.