Here is the situation:
1. The battery life of my GPS sport watch is, say, X hours.
2. The duration of my run, ride, or hike is expected to be greater than X.
This is unlikely to be the case for the longest of long training efforts, since even entry-level GPS watches last 8-10 hours. But in an ultra marathon, Ironman, expedition adventure race, 24-hour mountain bike ride, or multi-day backpacking trip, this situation is very possible, if not certain, especially for tougher courses and for slower participants.
So what am I to do? In this post, I will discuss five techniques to make a GPS watch last longer.
Since I am a longtime user of the Suunto Ambit2, the information here is most specific to the Ambit models. But the recommendations are relevant to other GPS watches, too, including those from Garmin and Polar.
Why should I care?
If my GPS watch will die before the end of my outing, it’s not necessarily critical that I take action. I may be indifferent to having incomplete data in my Strava profile, for example. And I might figure that, by the time my watch dies, I won’t need its quantitative data anyway — I’ll be relying on instinct to gauge my effort.
But, personally, I prefer that my watch remain useable. As an analytical (and anal) person, I like having a complete record for later analysis. More importantly:
In an ultra. I think that having the data — especially early on, but still late in the race, too — helps me to optimize my performance. A more experienced ultra runner may better know how they should feel at miles 70, 80, or 90, but I’m not there yet.
On a backpacking trip. My GPS watch is as helpful as my topographic maps when navigating, and generally more useful than my compass or handheld GPS unit. It helps me determine the distance to the next important landmark, the time to the next water source, the remaining vertical to a pass or summit, among other things. Also, when I return home, it’s useful to have a complete record of my track if I plan to repeat it or publicly share it.
A fastest known time (FKT) attempt would be another — albeit exceptional — instance in which I would want complete documentation.
Make a GPS watch last longer!
Five things you can do:
1. Buy or upgrade to a better watch
Entry-level GPS watches like the Garmin Forerunner 25 cost $150-200 and last 8-10 hours. Top-of-the-line watches like the Suunto Ambit3 Peak cost $400-500 and can last 20-200 hours, depending on the GPS frequency interval.
Refer to the battery life comparison chart for GPS watches that I published last week.
If at least occasionally my adventures will be longer than the battery life of an entry-level watch, I might quickly overlook the premium cost of a higher-end model. The nicer build and enhanced features offer additional value, too.
2. Mid-flight watch exchange
If I have another GPS watch (or smartphone with an app) that I can swap, I have effectively doubled the duration for which I will have data. This is a clean and fast solution, but not without pitfalls:
- It’s expensive, unless I borrow the second watch, or use an older watch that I held onto after upgrading to a newer model (which is lost resale money).
- The data will be recorded as two separate efforts — like a Monday and Tuesday run — which will complicate post-race analysis unless the files are merged. Refer to the comments for links to some online tools that will do this.
- Before the race, I will have to adjust the display fields and recording settings for two watches, which is a slight inconvenience.
3. Mid-flight recharge
On a backpacking trip, recharging my GPS watch is a no-brainer. I do it when I’m stopped — normally, in camp or at a long lunch break — and the weight penalty is minimal: the watch-specific power cable, plus a 3-oz Anker portable battery charger, which I use to recharge my smartphone-turned-GPS, too.
If I had to recharge my watch while moving, however, I would probably find another option. I have no interest in running, riding, or hiking — especially in a race environment or on semi-technical terrain — with a loosely attached wire dangling between my wristwatch and a charger tucked inside my pack or a pocket. Brian Lucido was forced into this situation during his FKT attempt on the Sierra High Route, and it sounded less than ideal.
WARNING. This technique may solve one problem (limited battery life) but it may encounter another: limited internal memory. My Suunto Ambit2, for example, can record about 25 hours of data at 1-second intervals. (This estimate is based on unofficial online sources; information from Suunto is hard to find.) If I try to record more data, the most recent data will overwrite the earliest data, thus defeating an objective in recharging the watch: to have a complete record of my outing.
Thankfully, with the Ambit there is an easy fix. In Movescount, I can change the recording setting to 10 seconds, from its default 1 second, which would create enough memory for about 250 hours of data.
4. Change the GPS frequency
Obtaining its precise location (i.e. a fix, in latitude and longitude) via GPS orbital satellites is the primary power drain on a GPS watch. Other hardware like the display, barometer, accelerometer, and heart rate receiver consume relatively little battery.
Most commonly, a GPS watch is set to obtain a GPS fix (and record that data) every 1 second. This frequency is adjustable on some watches, however:
- Garmin Fenix 3, Fenix 2, and Forerunner 920XT: 1, 60 seconds
- Polar V800: 1, 60 seconds
- All Suunto Ambit watches: 1, 5, 60 seconds
By increasing the GPS fix frequency, battery life is greatly extended. The aforementioned Garmin models last 50 hours in “UltraTrac” mode (60 seconds), versus the normal 20 hours, according to Garmin. However, there is a cost to a less frequent GPS fix: less accurate data. Read more about this tradeoff.
Personally, I have found that a 1- and 5-second interval is adequate for running, and that a 60-second interval is adequate for hiking. 60-second data of a run could be considerably inaccurate, as many twists and turns can go undetected between GPS fixes. In fact, in theory, if I ran at 7 minutes/mile pace around a 240-foot diameter circle, my watch would record zero distance, assuming that data from other hardware like the accelerometer and barometer/altimeter was not utilized.
5. Multi-sport modes
Among all the techniques mentioned, this is my favorite. The advantages:
- One watch
- One complete data record
- No mid-race recharge
- Maximum data accuracy, given the constraints of using just one watch without a recharge
I’m certain that it can be done with a Suunto Ambit, but less so with Garmin or Polar models. If you are more familiar with the advanced features of these models, please share.
In Movescount, I created three “Sport Modes,” and named them Ultra 1, Ultra 5, and Ultra 60. All of the settings are identical, except the GPS frequency:
- Ultra 1: “Best” (1 second), at which the Ambit2 has estimated battery life of 16 hours
- Ultra 5: “Good” (5 seconds), 24 hours
- Ultra 60: “OK” (60 seconds), 50 hours
During a race, I can change between Sport Modes on-the-fly by holding down the upper-left “BACK LAP” button. I can change the Mode (and thus GPS frequency) based the remaining battery life or on my desire for accurate data.
For example, I could race for 14 hours in Ultra 1 mode, draining my battery to about 12 percent, then change it to Ultra 5 to eek out another 3 hours (17 hours cumulative), or to Ultra 60 for another 6 hours (20 hours cumulative). Fourteen hours deep in a race and closing in on the finish, I’m probably relying much more on instinct than watch data, so the accuracy is less important. At the finish, though, I still have a complete record of my effort.
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