...The battery is forever going flat and it’s a 5 month old genuine Hyundai battery. It’s a Delkor 5523L.
Further to Gonz's post above, and just in case you didn't know, your battery is experiencing "parasitic draw" or "parasitic drain". Most vehicles experience a little battery draw, even if all the electronic components are turned off, but your battery has a nasty case of it.
Typically, the normal amount of parasitic draw is say, between 50~85mA (0.5~0.85A) in newer cars and less than 50mA (0.5A) for older cars (your 12-y-o car?).
You can get more information about the cause and the cure of this problem by looking it up on say, YouTube. I would limit myself to following videos posted by workshops, mechanics, battery manufacturers/retailers, or reliable contributors like "Chris Fix" or "Eric the Car Guy".
The usual steps are.
1. Using a multimeter, measure what is the battery's current draw, as explained by Gonz above.
2. Locate the source of the draw, which is often the most tedious part of the process.
I cannot remember whether your car's age (2011) makes it okay to pull out car fuses, one by one, until the multimeter registers a drop in the draw on the screen (which means that particular fuse controls the circuit responsible for the draw). On newer cars the "pull fuses" technique is often not recommended. See the YouTube videos.
Following
all of the numerous but simple steps is important to get the right result. For example, I switch off everything in the car; remove ignition key (and store about 2m away), let the car 'rest' for say, an hour (to let the car's computers go to sleep); ensure the boot is closed (so no boot light on); disable the bonnet switch, if fitted, etc etc.
