If my battery is only 3 yrs. old, why do I need to get a jump every so often?

First, a 3 year old battery can be something that should be replaced. Batteries should be tested to see what the state of charge is and the ability to sustain a load. 3 years is probably the median age of which batteries fail. So, it could be that it should be replaced. That said, no - running the motor for 20 minutes before driving will not flood the engine. And, running the motor at idle speed of 700-800 RPM is not enough to charge the battery. You need 2,000 RPM for a sustained period of time to recharge then battery properly. Have the battery professionally checked and go from there. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops