A mobile wireless communications device may include a device housing, and mobile wireless communications device circuitry carried by the device housing. The device may also include a removable electrical power supply module coupled to the mobile wireless communications device circuitry. The removable electrical power supply module may include a module housing, and within the module housing, a battery cell, a DC-to-DC converter coupled to the battery cell, and an output inductor coupled to the DC-to-DC converter. The removable electrical power supply module may also include, within the module housing, a spark suppression circuit coupled to the output inductor, and an output voltage clamp circuit coupled to the output inductor. The removable electrical power supply module may further include a pair of output terminals carried by the module housing and coupled to the output voltage clamp circuit.