:agree: what he said...
But, how do yo know your battery is good? I've seen bad batteries right out of the box, or they die in one season.
What is happening to your ski??
If it's dieing after it sits... look for a drain.
If there isn't a drain, disconnect the battery, and see if it goes flat. (in whatever amount of time you are having issues with)
If it's dieing while you are riding it around... then you could have a stator or regulator issue.
Give us more info on the situation.