provided on the low bat dead bat line and when the battery voltage reaches approximately 1 6 volts a dead battery indication is provided to the system over the low bat dead bat line a battery change backup circuit indicated within the dashed line to the right hand portion of fig1 provides a source of supply voltage for battery change the operation of the battery change circuit will be explained hereinafter the remaining portions of power system 13 include the voltage selection section and the supply voltage generation section the supply voltage generation section includes battery bt1 having its negative terminal grounded and its positive terminal connected to line v batt included in the supply voltage generation section is bipolar transistor t1 having its emitter connected to v batt its collector connected to one terminal of resistor r18 which is in turn connected to resistor r15 which is connected to ground a pair of switching transistors t2 and t3 are coupled in parallel for current handling purposes each of their emitters being connected to ground their collectors commonly connected and their bases commonly connected and coupled to the junction between resistor r18 and resistor r15 included in the primary current flow path of transistors t2 and t3 is inductor l1 having one terminal thereof connected to the commonly connected collectors of transistors t2 and t3 and its other terminal connected to v batt line feedback between the collectors of transistors t2 and t3 and the base of transistors t1 is achieved by a first path which includes capacitor c23.