Abstract: A portable energy source includes a case defining a battery compartment having an opening, a cover that covers the opening of the battery compartment, a power inverter mechanically coupled to the cover and adapted to be electrically coupled to the battery by leads disposed on the case when the cover is disposed to cover the opening of the compartment.

Abstract: A PWM-based controller for controlling a voltage applied to a DC-powered electric heating blanket from a power source includes a square wave producing circuit for connection in the circuit with the battery and the blanket. The square wave producing circuit produces a variable duty cycle square wave for controlling application of power to the blanket in accordance with the duty cycle of the square wave. The square wave producing circuit has a control input for varying the duty cycle of the square wave in response to a voltage at the control input. The voltage at the control input may be set manually using a voltage varying circuit connected to the power source. A low voltage detection circuit may also be connected to the power source and coupled to the control input of the square wave producing circuit for automatically producing a voltage that decreases the duty cycle of the square wave when the battery voltage decreases to or below a predetermined level.