Tell us about yourself!
Thank you for such a carefully planned instructable. It was clear and easy to follow, and very informative.
Yes, I have soldered directly to battery terminals. It's quite easy. And a soldering iron is a $10 tool, not to mention an extremely useful skill. Nearly every instructables on this site requires a soldering iron, or some tool that "not everyone has". If you gave it a try, rather than persisting to give reasons why attaching flammable object attached to a current-bearing wire in a child's toy is a good idea, you might discover that all of your googled objections were unfounded. You're only hurting yourself by refusing to learn a fundamental skill out of pride.
The addition of salt is a nice idea, but misled. The addition of a solute reduces the freezing point, it's true, but it also reduces the heat capacity of water. Meaning - while the water does get to a lower temperature, it actually takes less heat to raise the temperature. So you wind up at a net disadvantage compared to using distilled water (tap water has a high concentration of solutes).
This is far more effort than necessary. You don't have to create a battery shaped device. Simply solder the wires from the adapter to the correct terminals. This also makes the process more practical in devices which hold multiple batteries.
The topic isn't how to power a device in the woods. It's how to power a device without a battery. Every instructable on here requires tools. I'm not sure of the purpose of your question.
I'm sorry but going out to the hardware store for a bunch of wood and then sawing it, and then fastening some metal is simply not faster than soldering, which takes a fraction of the time, cost, and tools. Calling soldering unreliable is just plain silly, because you're calling the IEEE and NFPA wrong. It's the most reliable way to join two conductors.
Soldering is not permanent. The process of placing or removing the terminals, should you need to, takes seconds.