A modular, intrinsically-safe power module assembly is provided. The assembly includes a rigid conduit adapter configured to mount to a conduit of a field device. A housing, having an interior, is operably coupled to the rigid conduit adapter and is physically supported by the rigid conduit adapter. At least one non-rechargeable battery is disposed within the housing. Intrinsic safety circuitry is coupled to the at least one non-rechargeable battery, and is coupled to a connector that mates with a cooperative connector in the rigid conduit adapter.