The cheap:
http://www.supercheapauto.com.au/onl...spx?pid=283446
The not so cheap: Deep-cycle battery.
Do you have a cigarette lighter cable? My HEQ5 was supplied with one, not sure on the EQ6. If you do have one then the battery pack will be a simple plug-and-play. Should get you through the transit with some power to spare. And if your not going to use it often, then most defiantly go with the cheap.