Re: diy battery cables
Welding cables work well, they are designed for wet area use so they have a water proof sheath and are very flexible due to the fine pitch wire. I recommend sealing the ends with epoxy shrink tubing to keep them dry inside. They don't handle vibration as well as the thicker wire battery cable so make sure it is well supported.
If your using the boat in salt water buy the proper marine battery cable, each wire is individually tin coated throughout its length and resists corrosion much better.
