What is the reasoning behind the not rusty warning?

While I agree with the sentiment that it is technically stealing. No one should worry about charging their phone in public. Atleast in the region of the US I am located, it costs about 1-2 cents per year to charge your phone. So charging your phone for one sitting would be a miniscule amount of money. Just opening the door of the business and letting the conditioned air out would cost them more.

Obviously cars are an entirely different situation since one charge can be several if not tens of dollars.

I’m surprised I don’t see more people recommending KeePassDX! I agree and feel much more secure knowing exactly where my encrypted password vault is.

Also I recommend that people use Syncthing alongside KeePassDX so you can host your own cloudish environment to share the password vault between your devices. Keepass 2 is a great Windows/Linux application for interfacing with the .kbdx vault file format used by KeePassDX.