An electrical system is provided, including primary and secondary devices, the primary device including an electrical power source; a cavity to receive the secondary device; at least one electrical contact within the cavity to contact a corresponding contact on the secondary device when the secondary device is in the cavity, the electrical contact being electrically connected to the source; at least one data contact to transfer data between the primary and secondary devices; and a lid moveable between a first position to retain the secondary device in contact with the electrical and data contacts and a second position in which the secondary device is free to move out of contact with the electrical and data contacts, wherein in the first position the lid urges the secondary device into contact with the electrical and data contacts, and wherein the secondary device is keyed to the cavity of the primary device.