Auxiliary power is provided to an auxiliary heating, ventilation and air conditioning (HVAC) subsystem located compactly beneath the passenger seat of a daycab. Nickel metal hydride (NiMH) or suitably alternative battery power is inverted to drive the HVAC subsystem, and the batteries are charged from the daycab's alternator when the daycab's engine is running or from a roadside power grid when the daycab is idle.