Abstract: A battery includes: at least two jellyrolls; and a case. The at least two jellyrolls are disposed in the case, the case is arranged with at least two extension portions around a central axis of the case, and the at least two extension portions are communicated with each other. Each of the at least two extension portions is filled by a respective one of the at least two jellyrolls; the number of the at least two extension portions is equal to the number of the at least two jellyrolls.

Abstract: A charger, a device to be charged, and a charging system are provided, the charger includes: a power interface and a first charging contact surface; wherein an input of the power interface is coupled with a power supply, an output of the power interface is coupled with the first charging contact surface; the output of the power interface comprises a power supply positive output and a ground output; and the first charging contact surface comprises a first closed loop and a second closed loop, wherein the first closed loop and the second closed loop are configured independently of each other, the first closed loop is coupled with the power supply positive output of the power interface, the second closed loop is coupled with the ground output of the power interface, and the first closed loop and the second closed loop are configured with bare conductive areas.