David, I designed my sustainer to use a 12v battery (actually, an 8-cell AA battery clip). The components you use dictate the power you can use. The LM386 chip has a range anywhere between 6v (I believe) to 18v+, depending on the manufacturer and specific specifications of the chip (those voltages are estimates -- they can have a variety of values). Obviously, you would not want to use an 18v power supply for a 12v circuit, because reducing the voltage via resistors greatly decreased the efficiency of the battery. As for the cell phone type batteries, for the most part I think they are too expensive to use during this phase of research. Once this project is finalized, if ever, then we could start looking at alternate batteries. As of right now, however, standard off the shelf batteries are more cost efficient, I think.