According to an embodiment, a printer includes a battery, a display, a memory and a processor. The memory stores a predetermined residual capacity of the battery of the printer and amount information of a printing medium on which a predetermined printing data can be printed with the predetermined residual capacity in association with each other in advance. The processor controls the display such that the amount information corresponding to the predetermined residual capacity stored in the memory is displayed on the display, in a case where determining that the residual capacity of the battery is reduced to less than the predetermined residual capacity.