I have a double LGB powered Mallett that has 12 NiMh AA in for a voltage of around 14 volts. This is plenty for power and running time of around 4 hours. AA rechargeable ought to be easier to source if you have issues finding Lion. If course depends on what you are trying to power, but any battery size in the range of 12v ought to be more than adequate. I think we get hung on the DCC and other Voltages applied for not just conversion and signal (DCC) and normal DC, once you are into battery the voltage needs not be so high as there are fewer chances for voltage drop than with long wire tuns and possibly dodgy rail joints that we experience with Track Power.