On Tuesday, March 26, 2019 at 10:12:02 AM UTC-7, David Farber wrote:

I was testing the battery voltage where the battery holder's terminals
are soldered to the board.

Good. And, the usual self-test can/should exercise the chip that
keeps the timer running. It won't, necessarily, test the time accuracy,
and a typical such system uses a quartz crystal with a couple of
small capacitors. The crystal could be fractured, or (worse) one
of the capacitors could be shorted. Tiny capacitors, only gonna
be able to find 'em because they're next to the rock.