Need Help Please
 

I'm not sure it this is a battery or alternator problem don't worry i'm not just wasting everyone's time i did a search and nothing came up that i could find under my particular problem. The car idles great once it's warmed up but when my radiator fans and intercooler fan comes on i get a fluctuating idle up an down from 800-1000 rpm's i'm guessing it's the alternator any suggestions or similar problem would be great by the way i'm a running an Odyssey PC680 batter. Thanks