Update: The battery was weak, the charging system was fine - for a hybrid.

For those of us used to alternator behavior, the hybrid 12V charging system is different. It does sometimes turn off completely, leaving you with just battery voltage of 12V or less. To us old-timers that indicates a charging system problem. In a hybrid, it just indicates it is turned off at the moment.

Lifespeed

2003 Civic Hybrid 5 speed