With the right tools such as the EEVblog μCurrent and a good
multimeter, measuring the most minute current changes is a
simple task. But translating this into battery longevity isn’t
so cut-and-dried…the stated capacity in the battery datasheet
assumes a small and constant load, while the watch current can
vary greatly. What’s more, the relationship between current draw
and battery longevity isn’t necessarily linear. This gets messy.
Sometimes you just need to put math and theory aside, plug the
thing in and observe the actual outcome. To that end, we built a
test fixture to simulate a consistent use case: activating the
watch display once per minute and monitoring the battery voltage
as it declines, allowing us to objectively compare different
versions of the watch software. The raw data is logged to an SD
card for later review and conversion into nice graphs. So this
is primarily a tutorial on using the Data Logging Shield for
Arduino, but along the way there are some good ancillary tidbits
on hardware and