The way to check for an unwanted current drain is to measure with a multimeter across the battery with the car off. It's normal for modern cars to have a bit of drain (after all, the clock, flashing LED's, alarm, etc always draw power). But it should be small...something like 300 milliamps sticks in my mind.

No matter, just put the meter on the battery and pull fuses one by one. I would start with the in-car fuses rather than under the hood.

When you remove one that stops a great deal of current flow, look up what circuit you just disabled. Then look into that circuit.

My daughter had a new car that would drain the battery in four days...turns out it was a pinched wire on the trunk light (always ON)! Since then, I lie awake at night worrying if the light in the refridgerator is off...