For F4E/F90X For added power especially during prolonged or low-temperature shooting, the Nikon F4E or F90X can count on the DB-6, which uses six D type batteries, as an alternative power source. The DB-6 connects to the F4E or F90X via the Nikon External Power Cord MC-28 or MC-29 respectively. For added power, especially during prolonged or low-temperature shooting, the Nikon F90X can count on the DB-6, which uses six D-type batteries, as an alternative power source.