My ATV will only run on the battery if the battery is dead it won't start, hook it up to a battery charger and it will start and run, but disconnect the charger and it dies instantly(unless the battery is charged). Is this the stator or alternator, or could it possibly be something in the wiring. Also the ground wire is corroded and needs to be replaced I don't know if that would cause this problem.
The Atv is a 1995 honda Foreman TRX400FM

 

First thing is to replace what you KNOW is bad, start with the ground wire. It is obviously not charging the battery, or has a ground somewhere it shouldn't. It's unlikely there is an internal problem (stator or rotor), more often it's the voltage regulator/rectifier or a wiring problem. Make sure the battery will accept and hold a charge, it may be toast as well. The best thing you can do if you're going to fix it yourself is get a proper manual, mine is a Clymer from Canadian Tire ( $39.99 Can) The Honda shop manual is better, but a lot more money. If you're good with tools and understand DC electricity, with the manual you've got a good chance of sorting out the problem, if not it's a good job for someone that does.