A universal chassis frame is disclosed having a ladder-frame construction configurable to position a rear axle(s) at variable distances from a back of a vehicle's cab to provide customized rail/bed lengths for different electric truck classes. The chassis frame includes a central frame having a pair of main frame rails to support at least two battery modules substantially within an intra-frame space. A front subframe supports the cab, a front portion including a pair of upper frame members mounted above the corresponding main frame rails, and a front axle unit mounted under the front subframe. A rear subframe supports at least one rear axle unit mounted under the rear subframe and any of multiple configurable rear payload units via a common connection interface affixable to the main frame rails so the rear subframe's location with respect to the main frame is longitudinally variable from the back of the cab.