Small Engines (Lawn Mowers, etc.): snapper lx1642h, model engine, voltage regulator

Question
got mower, mowed lawn no problems. went to start mower to mow again mowed great until about 15 minutes and the blades quit turning, and batter light was had come on(engine still running fine) replaced battery and mowed great about 2 times, then battery light came on again, and blades quit turning and it will not turn over now, if i charge my battery it will run and mow great but after a while the blades will quit turning and it will not turnover at all? any ideas? something like alternator not charging the battery? but dont know much about lawnmowers(from ky also)
thanks

Answer
Yes, it sounds like it is not charging, the alternator is under the flywheel, and may or may not have a voltage regulator, but to be of more help, I need to know what brand and model engine you have.
So if you could find those numbers, that would be real helpful.