Is the needed voltage output important for the simulation?

HOMER does not model the voltage of the DC bus, so you don't need to specify the bus voltage.  However, you should take the DC bus voltage into account when specifying the quantities of batteries to consider.  For example, if you are using a 6V battery and you choose a 24V bus voltage, you'll have strings of 4 batteries in series, so the number of batteries in your battery bank could be 0, 4, 8, 12, 16, and so on, but not 3 or 10 or 11.  For that reason, you should only enter multiples of four in the "sizes to consider" table on the Battery Inputs window.  Similarly, if you choose a 48V bus voltage, you should enter only multiples of 8.