It's the same principle, just a different application in the link.
Yes, if you leave a 12V battery connected to it and forget about it, you'll eventually boil it to death. It may take a short time or a long time to kill it, though, depending on the exact battery tech, capacity, and other...
Yep, it's normal for an unregulated supply. Here's a pretty good explanation of what that means, some math included:
Regulated vs Unregulated Power Supplies
A short and highly oversimplified summary: An unregulated power supply is a straight ratio of the source voltage. Generally speaking...