For a while, it looked to me like my bicycle's rear-light was “somewhat” dim. I supposed that the batteries might be getting low, but I was not sure.
So, given that I have a multimeter, and that the internets give ~20%
decrease in voltage as reasonable limit for a non-recheargable battery
that is not "dead", I set to measure. The batteries are type
N Battery (which were not as common as I hoped, at
least not as common as either
C, all of which I
could find at the nearby store, but not
Battery "marked" voltage:
1.5V. New batteries (after I replaced
1.451V (good enough). My old batteries…
Ouch! That's ~30% decrease. No wonder I could stare in the light without problems With the new batteries in, it's a bit painful to look directly into the small light.
In hindsight, 3 years of light (pun intended) use is more than reasonable.
So note to self: test batteries more often, at least at the beginning of the cycling season.