What are the most important considerations when deciding which GPS sport watch to buy? Features, fit, and price — most definitely.
But don’t overlook battery life, especially if your workouts, competitions, or adventures often exceed the duration of a long workday, as is the case with ultra marathons, Ironmans, expedition adventure races, 24-hour mountain bike races, multi-day backpacking trips, and other long-distance activities. Even if you prefer shorter outings, a robust battery is still a perk: like a new cell phone, it will need to be recharged less often.
If your GPS watch battery dies before you’re done, at a minimum you’ll have an incomplete record of your effort. (And you know what they say — If it’s not on Strava, it didn’t happen.) But it could be worse: without access to data like pace, heart rate, distance, coordinates, or elevation, you may struggle to maximize your performance and/or to navigate.
In this post I discuss the factors that affect the battery life a GPS watch, and provide a battery life comparison chart for GPS watches. Skip to the comparison list.
Battery life basics
The power capacity of a battery is measured in ampere-hours, specifically milliampere-hours, or mAh. A battery with more mAh will last longer than one with less, all else being equal. For example, the Suunto Ambit2 features a 480 mAh battery whereas the Suunto Ambit2 S has a 240 mAh battery. Not surprisingly, the battery life of the Ambit2 is about twice that of the Ambit2 S: 16 hours versus 8 hours with a 1-second GPS recording interval.
But “all else being equal” is seldom the case, so mAh is not the sole determinant in the battery life of a GPS watch. For example, the Polar V800 has a 350 mAH battery, yet its battery life is about the same as the Suunto Ambit2. I don’t have a precise explanation, but no doubt it’s due to differences in hardware and software.
GPS recording intervals
The primary drain on the battery of a GPS watch is the recording of its precise geographic position (i.e. a “fix,” measured in latitude and longitude) via GPS, which requires communication with orbital satellites. Other hardware like the display, barometer, accelerometer, and heart rate receiver consume relatively little power.
The frequency at which a GPS fix is obtained — known as the GPS recording interval — is either fixed or adjustable, depending on the watch. All Suunto Ambit watches can be set to 1-, 5-, or 60-second intervals (“Best,” “Good,” “Okay”), for example. With longer intervals between GPS fixes, the battery lasts longer. For example, the Garmin Fenix 3 lasts 20 hours with a 1-second interval, but for 50 hours in “UltraTrac” mode (a 60-second interval).
A fixed, non-adjustable interval limits the ways in which the battery life can be extended, and — I would add — the watch’s applicability for long-distance efforts.
Unfortunately, as the GPS interval recording increases, the accuracy of the recorded data — e.g. route, pace, distance — decreases. For instance, when running at 7 minutes/mile pace, a watch will record its GPS location every 12, 63, and 754 feet when set to 1, 5, and 60-second intervals, respectively. During these longer durations between recordings, obviously there can be more undetected twists and turns. Data from other hardware can improve accuracy between the GPS fixes, but the watch will mostly assume a straight-line distance between recorded positions.
In the market for a GPS sport watch, and wanting to compare estimated battery life? The chart below is for you. Estimated battery life is based on manufacturer specs; the figures have not been independently verified.