As others have said, as close to the batteries as possible with heavy gauge wire. What has not been said is how heavy do you need to go? As a minimum you should consult the install instructions of the manufacturer, which will indicate a minimum wire gauge and maybe distance to the batteries. A better approach is to know you should look for no more than .75 drop in voltage and calculate by looking at one of the many wire gauge voltage drop tables on the web. Typically these charts will give a factor to multiply by each foot for different gauge wires. What also has not been mentioned is the need for some ventilation, but any unit you buy, the install instructions will indicate the requirements which you should pay close attention to.