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Runner’s Tech: Get the Most out of Your GPS Battery

Posted Feb 28 2012 9:57am

Does your Garmin not hold its charge no matter what you do? Sending it in for repair will result in weeks of training without a watch; and buying a new one is out of your budget. Yet it’s impractical to use a watch that gives up before you do. Or perhaps you just got a brand new GPS watch – and you want to prevent all this from happening. As it turns out, there are a few things you should know about the battery in your GPS device. Below are some of the most overlooked facts about rechargeable lithium-ion batteries (Li-ion Li-poly) found in most GPS watches, including all Garmin models , Nike+ SportWatch , and MOTOACTV . As a bonus, you can also apply this knowledge to other personal gadgets such as cell phone, laptop, tablet, or GPS navigation device.

Discharge: A common myth surrounding rechargeable batteries suggests that it’s beneficial to drain them periodically. Fully discharging a battery – or deep cycling - is believed to reset or refresh ions in a battery, and thus clear a bettery’s “memory” to be recharged as a new unit. The truth is, this only applies to  nickel-based batteries . All GPS watches from Garmin – and almost all other brands on the market – use lithium-based battery which does not require regular discharging. In fact, the longevity of a lithium battery is directed affected by the number of times that it’s been discharged and recharged. In other words, the more frequently a lithium-ion battery is discharged, the shorter its lifespan will be.

Storage: Another big concern about the battery life of your GPS device is whether to leave it plugged in while not in use. The common misconception is that it’s bad to do so, because it will overcharge the battery and somehow shortens its capacity. This is not always the case. As explained above, lithium batteries lose their ability to hold a charge after numerous cycles of usage. Moreover, if a lithium battery is not in use, it slowly loses power, as if you’re using it. This means keeping a lithium-ion battery plugged in can reduces the number of charge cycles, and increases its longevity. For more technical info, check out  Dan’s Data  regarding lithium battery on laptops.

However, keep in mind that keeping your battery fully charged or plugged in for a prolonged period of time has consequences. As pointed out by  Battery University , “high charge levels and elevated temperatures hasten permanent capacity loss”. The bottom line is: it’s okay to keep your GPS device plugged in if you use it frequently; but it’s a better idea to leave its power at around 40% for the duration of a prolonged of inactivity.

Environment: Temperature, of both operation and storage, is a huge contributing factor to a lithium battery’s performance. Garmin’s  Important Safety and Product Information  suggests:

  • When storing the device for an extended time, store within the following temperature range: from 32°F to 77°F (from 0°C to 25°C).
  • Do not operate the device outside of the following temperature range: from -4°F to 131°F (from -20°C to 55°C).

Most people should be able to stay within the above constraints – unless they partake activities in extreme conditions. However, it’s important to remember that combination of heat and high charge is the worst enemy of a lithium battery. That is to say: don’t leave GPS devices in your car or on your windowsill in direct sunlight, especially during warm seasons.

Calibration: This is not to be confused with what’s described in the first section above. Sometimes a battery is in good health – but it appears to be otherwise. You may notice that no matter how long you charge your GPS watch, its battery capacity can never reach 100%. As it turns out, this is caused by a synchronization error, developed over time, in the GPS software. This issue has been explained and addressed by Garmin Support at  Running Free . Below are the steps to re-calibrate a battery and software:

1) Charge your Forerunner 405 to 100%
2) Remove the Forerunner 405 from the charger
3) Start the timer on your Forerunner 405
4) Allow the Forerunner 405 to completely drain
5) Charge the Forerunner 405 back to 100%
6) Wait one additional hour
7) Remove Forerunner 405 from the charger

Keep in mind these instructions work specifically for the Forerunner 405, or possibly older models such as the 305 or 205. It is unclear whether Garmin has addressed this issue in updated firmwares, or other recent models. However, if you own a Forerunner 405 (or older model), this could be worth a try before you call costumer service.

Are you aware of the facts mentioned above? What’s your experience with battery life of a GPS watch? What are some other tips that may help you get more juice out of it?

- Kevin

(Kevin Lu is an engineer, currently working in the field of orthopedic devices. He received his B.S. and M.S. in biomedical engineering from New Jersey Institute of Technology. Science, technology, and running are Kevin’s passions. In his spare time, Kevin trains for and participates in races of various distances. His recent personal records include 20:58/5K and 5:48:22/50K. Follow him on Twitter (@ SweatEngine ) and check out his blog Beyond Distance .)

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