If you look at the battery specs youll find either CA or CCA (Cranking amps)
This is the maximum amount of juice the battery will throw to the starter motor for at least 30 seconds.
Your never ever likely to exceed this from the battery, even when starting with thickened oil on a cold day as these bikes dont really take a lot to kick over.
Lets look at the NC24.
This bike has a bigger batter than the NC30 as stock and will supply 80A Cold crank current (EN)
Manufactureres use the smallest possible wire gauge as copper is expensive.
You only have to look at the size of the wire from the Battery +ve to the starter motor solenoid to see how thin it is, granted it is a really short run. Cant you recycle some old starter motor cables? They carry the full battery load and are of a good length?
Looking at this chart 4 gauge would be idea as it is chunkey.
http://memcarnew.dev.archermalmo.com/su ... age-chart/
However, I would personally use some 8 gauge like this
http://cgi.ebay.co.uk/8-Gauge-AWG-10mm- ... 25606ac61f
10.00gbp for 5 meters, should be more than you need and isnt too chunky.
Its quite cheap and since your only likely to hit peak output when starting which isnt too long the continious power of the cable will be less.
