From the numbers given, they are intended for a nominal 6 volt supply. You could wire as many as you like in parallel, only problem being getting them the right way round. Running them on a higher voltage requires something to limit the current into the parallel array to result in 6 volts presented to the array. Once you know the current of the total, you can just use Ohm's law to work out the value of the resistor. (Battery voltage - 6 volts, divide by the current in Amps, answer in Ohms). Once you know the voltage dropped across the resistor and the current through it, you know the power rating it needs.
You could also use a voltage regulator chip. LM7805 gives 5 volts at 1A, if that's not bright enough, there are adjustable types.