[Tinker]

When it fails, carry a volt meter with you and take a look at the current battery charge to see if it's drained. If you are running a 12v battery (I didn't see that in your description) on a 6volt electrical motor system. Well I'm no help to de-dug the long list of things. Is it a 6v starter? Cables should not have a huge issue less you are cranking a ton. I use 00 welding cable on my 6v battery cables. Fairly easy to see if the battery is being charged with a volt meter.

How do you get it home? wait 30 minutes and then it works? Do you flatbed it home and charge the battery and all things are fine for 20 miles.

You still have fuel to consider so get out the check book. I'm just kidding. but...