One problem related to battery has been reported for the 2009 Hyundai Elantra. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2009 Hyundai Elantra based on all problems reported for the 2009 Elantra.
Panic alarm engages on its own (while parked) in driveway or work parking lot. Checked all doors, hood, trunk to ensure they were closed. Has not happened while car is in motion. When using key fob(manuf supplied) problem still persist. Press lock dr button(30-40 min later) alarm sounds,press unlock button(40-60 min later) alarm sounds or does not come on again. Press lock button to secure car, doors click twice but alarm engagement sound or light verification does not happen. This happens at random so I am sure if taken to dealer it will not happen or they will not confirm it is happening. I can not see any loose wires, blocked contacts or anything that might cause problem. Don't think it is the battery. Its has to be a short or a computer problem.