An approach is provided in which a battery cartridge aperture is included in a device. The edges of the battery cartridge aperture form a shape that match a selected battery cartridge and indicate a power configuration. The selected battery cartridge is selected from a variety of different battery cartridges with each of the battery cartridges having a unique external shape with each unique external shape corresponding to a different power configuration. The various battery cartridges each have a different configuration of battery cells within the battery cartridge that provide power to the device through electrical contacts. The contacts are affixed within the device with each of the contacts positioned to correspond with electrical contacts from the battery cartridge. In one embodiment, protective covers are provided that cover the contacts with the covers automatically retracting to expose the contacts when the battery cartridge is inserted in the device.