5.9, turn the key, all power shuts off, have to "reboot"

So my 5.9 has 185k miles, it was my daily driver for years, but now it's spends almost all of its life in the driveway. Lately I've been having an issue where I turn the key to start it, and click, all power dies. No interior lights, dash lights, nothing, regardless of key position. Disconnecting/reconnecting the battery resets everything and power comes back normally, every time.



Could the cold temps play a role?

Is there a relay that may be sticking open or something like that?

Could a weak battery charge cause it?



Any ideas?