just copied this from another site:
with the engine running you should have between 13.4-14.5 volts going to the battery. let the engine get good and hot, and recheck the charging system. voltage maybe lower but should be still in that range. as the wiring gets hot, it expands, and problems may not show up until then. if that's OK, charge the battery. most cycle shop can load test the battery for you, or after the battery is good and charged, leave it sit or 8-10 hrs. BEFORE trying to start the bike, check the standing voltage. you should have over 12 volts. if not battery is bad. if OK, hook it up to the bike and with a meter hooked up, crank the engine over, and watch the voltage. voltage should not go under 10.5 volts when cranking, if so, bad battery.
hope this helps.
