For fitness enthusiasts or serious athletes, a wristwatch equipped with GPS and sports-oriented functionality can be a potent training tool. Garmin's line of Forerunner GPS-enabled watches is a case in point, providing a range of features to measure your activity and performance. While ordinary watches will last for years on a standard battery, the Forerunner series requires a rechargeable lithium-ion battery to support its powerful features. Battery life is variable, depending on the model and your usage.
Garmin Forerunner watches charge through a set of contacts on the watch's surface. Once you've unpacked the watch, clip it into the charging mount and ensure the phone's contacts line up with those on the charger. Insert the charging clip's USB cable into the AC adapter, and you'll see a graphical battery-charge indicator appear on the screen. Most Forerunner models will charge fully within one to two hours, and will display an onscreen message to let you know charging is complete. If the watch or charger should get wet at any point, dry it carefully before the next charge.
Once the battery is charged, you're ready to begin training. Forerunner models vary widely in their features, but most will provide you with a wealth of information about the distance you've traveled and your rate of speed. With optional accessories, they can also monitor your heart rate, cadence or stroke rate. All of this sampling and data handling, especially when the GPS is in use, requires power. The battery in most Forerunners will last for up to eight hours of continuous use. The high-end 910XT will last up to 20 hours.
Power Saving Mode
If your training regimen is more modest, you can coax significantly greater life out of your Forerunner's battery by using the power saving mode. This setting shuts off the GPS receiver and other data functions, leaving only the watch circuitry active to maintain the date and time. In this standby mode, a single charge can last weeks. The Forerunner 410 provides up to two weeks' charge life in power save mode, the 210 up to three weeks, and the 610 up to four weeks. Each hour of active training during that time will reduce the remaining charge life proportionally.
Using Wireless Features
The GPS receiver, and the processor that calculates your position from the satellite signals, account for most of the watch's power consumption. For users who want to extend their life per charge as far as possible, some models can provide speed and distance data using only external sensors such as the optional foot pod or bicycle sensors. These transmit data to your watch wirelessly, and have their own battery power. By turning off the GPS and relying solely on data from wireless sensors, one athlete/blogger was able to stretch the 910XT's life per charge from an estimated 20 hours to 55 hours of tested training time.
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