Thanks for the pointers, guys. Given all the prompts about the battery, I went out this morning and checked the connections. They appeared to be pretty solid, but everything was still dead. No lights, no anything.
Still, I pulled the negative, reset it, and locked it down tightly. Problem solved, or so it seems.
I'll keep an eye on this, because I still have suspicions that the battery may be weak as Pawned alluded to.