# Garmin 500 & Garmin External Power Pack test



## xxxxx (Aug 29, 2011)

Hi All,

I needed to increase the battery life of my Garmin 500 to a minimum of 35 hours so I searched here and found some posts regarding home-made external battery packs. However, I didn't want to risk me screwing that up so I went with the Garmin branded product which is actually a Powermonkey product. 

Garmin:
External Power Pack 
010-10644-02 

I tested the Pack over 2 rides (2:30 and 2:00) with GPS and backlight. Then left it running between rides with the GPS and backlight on. 

I set the Pack to "Always On" basically the head unit used the Pack until it died then took power from the internal battery. The external pack died at about 27 hours 22 minutes of cumulative use. Upon depletion of the external pack the head unit showed a message: "External Battery Lost", (or something close to this phrasing). 

The internal battery took over seamlessly. The internal battery is advertised for up to 17 hours of life. During this test the internal battery went 14 hours 40 minutes.

On a dry ride no concerns of keeping the two pieces connected for the entire ride. In wet or muddy conditions I will be concerned of contaminants getting into the plug area. 

After one full charge to depletion test the Garmin/Powermonkey unit lasted 42 hours. 

I wanted to know if disabling the GPS would extend that battery life. I did a test of the head unit only with the GPS disabled and got 19 hours full charge to depletion. That tells me the GPS does not affect the battery life significantly. I'm not sure if I had the backlight on for that test.

Any thoughts or questions will be appreciated. Thank you.

Josh


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## Harold (Dec 23, 2003)

27.4 hours to 19 hours not significantly different? It is different but not the way you might expect. Redo that test. The first one too. Ensure consistent conditions between all of your trials.


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## xxxxx (Aug 29, 2011)

NateHawk said:


> 27.4 hours to 19 hours not significantly different? It is different but not the way you might expect. Redo that test. The first one too. Ensure consistent conditions between all of your trials.


I must not have been clear. The external battery pack died after 27.4 hours the internal battery in a stand alone test without GPS lasted 19 hours. I meant not that much better than advertised. However, the 14.7 hours the internal battery lasted after the external pack died does indicate that the GPS pulls a measurable amount of power.

The Garmin/Powermonkey did the trick but, can I count on it for my only distance measuring device in an important event? Or, should I also attach a Cateye bike computer as a backup? Backlight is necessary so that narrows down the choices.

Thanks for your response.


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## Harold (Dec 23, 2003)

sorry. 14.7hrs with GPS and 19 hours without. The difference between those measurements is over 4 hours. That's an increase in battery life of almost 30% over the gps-on condition. That is a pretty sizable increase in battery life. However, there aren't enough measurements to tell if it's significant or not. Either way, you should do those tests multiple times, ensuring consistent conditions, to see how much of a difference there is. If you left the backlight on for gps-off, the difference should be greater. If not, the difference should be repeatable. But we need to know how much variance is in the repeated measures before we can call something significant or not. If there's a ton of variance in repeated measurements, then any "significance" between these two numbers would be just noise. If not, then it matters if your end goal is maximizing battery life.

With that said, since your cutoff is 35 hours, the GPS on test that lasted 42 hours should work out for you with a little wiggle room. However, if you really are interested in pushing the limits of this setup, I'd look at taking multiple samples.


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## xxxxx (Aug 29, 2011)

I'll have more data in a month or so but I doubt I'll work toward a super accurate test. I hope this dats might help somebody.

Thanks for your thoughtful resonse.

Josh


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## ghettocruiser (Jun 21, 2008)

I'm just mildly alarmed that you are riding for 35 hours straight. 

Is this for randonneuring or ultra purposes, or multiple days without overnight charger access?


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## xxxxx (Aug 29, 2011)

I'm a Trans-Iowa V9 rookie. I hope to make the 2nd check point. It feels too audacious to hope to finish. 33 hour time limit for the 330 miles of Iowa gravel.

Thanks for asking.

Josh


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