I believe the anti theft warning light drains battery?

Hello,

The anti theft warning light does have the capacity to drain the battery, but it should take longer than a week.
Please note that every vehicle has certain amount of parasitic drain in the electrical system. Which will make the battery loose charge overtime and go completely dead after a certain period of time. That time will depend on the components of the electrical system of that particular car.
However many times you can have excessive parasitic draw/drain in your electrical system due to a faulty component. Like a glove box light staying on or a shorted window switch etc.

You can check and measure the parasitic draw by using a multimeter.

The Parasitic Draw (Current Drain) specification for your vehicle : Less than 50 milliamps (0.050 amp)

Here is a helpful video of how to do that task:

https://youtu.be/z5F7WpgjaRs

https://www.2carpros.com/articles/car-battery-dead-overnight

Please let me know of any questions.

Thank you.