mosfet 74 is in its on state so that when the switch 66 is pushed current will flow through the light emitting diode 72 thereby providing an indication of normal operation conversely when the terminal voltage of the batteries is low and the battery packs 10 20 are connected in series i e 34 stacked 34 the signal on the lead 48 is low and the mosfet 74 is in its off state so that pushing the switch 66 will not result in current flow through the light emitting diode 72 the mosfet 76 is provided for electronically indicating the operational state of the battery supply to the electronic equipment to which it is connected this electronic equipment is connected to the mosfet 76 via the 34 on reserve 34 terminal 78 within the electronic equipment there is a pullup resistor not shown under normal operating conditions when the signal on the lead 48 is high the mosfet 76 is in its on state its drain will therefore pull the external pullup resistor to a low state when the battery packs 10 20 are operating in the 34 stacked 34 mode the signal on the lead 48 is low and the mosfet 76 is in its off state therefore its drain will be pulled to a high state by the external pullup resistor thereby indicating that the battery supply is operating 34 on reserve 34 accordingly there has been disclosed an arrangement for automatically connecting a.