Chances are, something was pinched and is shorted. The best way to limit where the problem is coming from is this. Connect a volt or multimeter between the negative battery terminal and the negative battery post. The red connector on the meter will go to the battery post and the black wire to the battery cable terminal. At that point, you remove one fuse at a time from the fuse box under the hood to see which one stops the electrical draw. At that point, we will have narrowed it down to a specific circuit. If this started with the head gasket replacement, we'll know what to check.
If I had to guess at this point, I suspect there is an issue with a wire at or near the alternator. But testing will help us narrow things down.
Here is a link that explains this in more detail. Note, the aforementioned directions are later in the link after the basics. Basically, it will be the last paragraph.
Make sure the battery is recharged before starting this, all electrical components are off, and doors closed. The link will explain the procedure in more detail.
Let me know what you find or if you have other questions.
Tuesday, October 12th, 2021 AT 8:23 PM