As the counterparts of alternators, the auxiliary power modules (APMs) in electric vehicles (EVs) play an irreplaceable role in bridging the high-voltage (HV) propulsion system with the low-voltage (LV) auxiliary system. With the increasing demands of fast charging, the HV propulsion system is seeing an evolution from the 400 to the 800 V system. Adapting to such trends, the APM faces the challenge of a much wider input voltage range, particularly in EVs with a reconfigurable battery pack. This article proposed a reconfigurable current-fed dual active bridge (CFDAB) based converter. It accepts a record-wide input voltage from 180 to 900 V and an output voltage from 6 to 16 V. The closed-form solutions of switching current are with consideration of coupled inductor current, the key characteristics of CFDAB, and simple control to secure zero-voltage switching and minimize the switching current. Design implementation is also discussed in this article. A 3-kW prototype with a peak efficiency of 97% was built and tested. The experimental results proved the feasibility of using the proposed topology and control for the ultrawide APM applications.