Hi, Let me see whats going on here and help get you on your way to fixing up your machine. It sounds like either the voltage regulator or the alternator has gone out on you. I will need the full model type and code off the engine to give you the spec on how to check those items. Also look at the wires coming out of the alternator ( which is under your flywheel and let me know how many wires you have and what colors they are.
Also if you would like I can send you a link to a great guide that has step by step directions to check you r charging system. Its pretty detailed which is nice. http://www.briggsandstratton.com/support/frequently-asked-questions/engine%20charging%20voltage%20output%20specifications/~/media/08A3C4EB354246D995C3D5A5CC42D76A.ashx