The Hotshot battery power for Graflite would plug into "battery" after batteries are removed, for external power, but this is apparently no longer available. Could a regular 9 volt Dry Cell be hooked that way? I can't find a battery case extender for additional power. The manual says the Graflite 3-cell (D) will power two flashes, or three bulbs with an added 1.4 volt, making 6 volts--which is same as a Dry Cell, yes?