An external battery device is implemented which can detachably engage with a smartwatch to thereby enable seamless battery replacement and smartwatch battery replenishment without having to remove the smartwatch from a user's wrist. The external battery device can be a bezel that aesthetically fits in a cut-out around a perimeter of the smartwatch's face and locks in place using, for example, a male-female connection mechanism. The external battery device includes a casing that functions as the bezel for the watch. The casing includes a channel inside which a rechargeable battery is positioned. The male connectors of the external battery device extend downward from a hole in the casing to engage with corresponding female receptacles on the smartwatch. In typical implementations, two different shapes of the male and female connection mechanisms may be used to provide a consistent manner in which the user connects the external battery device to the smartwatch.