My 2010 Hyundai Elantra won't start without a jump

Had a Rav4 do same thing. I thought it was alternator. Took ground post off while running turned headlights on at same time but it keep running, so not alternator. advance said no not bad battery, but I put a new one in no more trouble. Hope it helps.

That sounds like an empty battery. Now the question is, is the battery just empty or is it in need of replacement.

After jumpstarting, you should drive the car for about half an hour-45 min. That's enough to charge the battery. Then stop the engine and try to start again. If the engine starts, chances are the battery is still usable. If it doesn't, it's time to replace the battery.