Hyundai Elantra battery

My 2009 Hyundai Elantra Touring won’t start after 10 minutes with the key in the ignition, car off, but lights on. Starts up right away with a jumpstart. The dealer says this is normal. The battery has died before after 20 minutes with the lights and radio on. Even this seems unreasonable. What gives? The car has less than 20,000 miles.