small word of caution. The wire should be twisted. Don't run it near the alternator, and don't zip tie it to a battery cable. The twist help keeps it from false triggering from induction that can occur if you don't.
You can buy a 6' extention from Jegs or Summit for about 12.00 with the ends. Pt # 8860
If you need something longer, you can buy just the ends to make up your own. Pt 8824