A method for calculating a remaining capacity of a battery includes: recording a sleep time of a battery monitor in sleep mode; reading an open circuit voltage measured and stored in sleep mode when the sleep time is greater than a preset time period and determining a first remaining capacity ratio based on the open circuit voltage; calculating charges consumed based on a preset current and the sleep time; calculating a second remaining capacity ratio based on charges consumed, a stored first remaining capacity value and a preset total capacity; reading values of battery parameters; determining a third remaining capacity ratio based on the values of battery parameters; and determining a current remaining capacity ratio based on the first remaining capacity ratio, the second remaining capacity ratio and the third remaining capacity ratio.