Estimate smartwatch battery life by usage.
Battery life is capacity divided by average draw, and on a smartwatch that average is dominated by GPS. Splitting the day into idle hours at a low milliamp draw and tracked hours at a much higher one shows why an hour of GPS can cost as much battery as most of a day of idling. The GPS-only runtime is the figure that matters for long events such as a marathon or a hike.
Wearable battery runtime
Daily drain = (24 - GPS hours) x idle drain + GPS hours x GPS drain; days between charges = capacity / daily drain
These figures are estimates based on population-average formulas and are intended for training and recreational planning only. They are not medical advice. Consult a qualified health professional before starting or changing an exercise programme, particularly if you have an existing medical condition.
The receiver and the processing behind it draw several times what background sensing does. An hour of tracking commonly costs as much as a day of ordinary wear.
Always-on displays, continuous SpO2 and heart-rate sampling, notifications and cold weather. Raise the idle drain figure to model those.
Yes — lithium cells typically retain about 80% of capacity after a few hundred cycles, so a two-year-old watch will fall short of these figures.