Today I have a 2007 Yamaha Grizzly 700 in the shop for an electrical problem. The machine would run fine, but it was not keeping a charge in the battery. I checked out the battery and the main electrical connections. Everything seemed fine so I moved on to the voltage regulator and stator. There is really no way to test the regulator, but it is easy to check the output of the stator. With the engine running you should see 20 to 30 volts ac on the stator leads. This one showed no voltage.
When I pulled the engine side cover off it was obvious that the stator was bad. In the photo you can see burned section on the right. I did a little looking around on the ATV forums and discovered that these Grizzly 700s frequently burn out the stator at about 4000 miles. This machine made it to 5500.