Abstract: A battery runtime extender may be configured to provide electrical power to an electronic device via electrical terminals disposed internally to the electronic device, such as within a battery compartment. The battery runtime extender may physically mount to the electronic device via fasteners associated with the battery compartment of the electronic device, where the battery runtime extender forms a seal between the housing of the battery runtime extender and the battery compartment of the electronic device that is resistant to ingress of water and/or dust. The electronic device may be configured to be mounted to equipment worn by or otherwise carried by an individual, such as a protective helmet. The battery runtime extender further provides electrical power capacity greater than would be provided by battery cells installed within the battery compartment.