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Garmin Geko201 and rechargeables?!


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Hi there!


As i were recently buying AAA sized batteries on a weekly basis, i finally ordered a nice set of NiMH rechargeables (750mAh) and run into a funny software problem of the Geko201.


In the Setup->System menu of the unit, you can switch the battery type from Alkaline to NiMH. Ok so far so good. This makes sense, as an Alkaline battery has a nominal voltage of 1.5V, while rechargeables mostly have 1.2V and you should get a reasonable battery-voltage-bar display with useing both types.


Ok, and now the odd thing: If i use the NiMH set for 2hours, the battery bars drop down very quickly, with the setup switched to NiMH, but if i switch the setup back to Alkaline, i immdediately gain two bars in the battery display.


Could it be, that Garmin mixed up the labels and the Alkaline setup is in reality the NiMH setup and vice versa?!


I´m just wondering...





P.S.: Software version is V2.20

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Kind of strange that you mentioned 750MAh - most NiMH batteries now fall into 1600-1850MAh range, and 2200MAh are out (http://www.thomas-distributing.com)

There is a wealth of info on batteries in the forums, you can use Find tab, search for "NiMH"


Here is an interesting FAQ: http://www.greenbatteries.com/documents/Battery_FAQ.htm


Happy trails,


http://www.quakemap.com - redefining Easy...

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Originally posted by quakemap.com:

Kind of strange that you mentioned 750MAh - most NiMH batteries now fall into 1600-1850MAh range, and 2200MAh are


Tobias was talking about AAA batteries and not AA's. Highest AAA mAh rating I've seen last time I checked was 750-800.

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SergZak is right. I was talking about the even smaller AAA sized batteries. Geko units all use AAA size, while the eTrex series uses AA.



However i was just wondering, if anybody else has seen that strange behaviour. Personally i will stick to useing the "Alkaline" setup for my NiMHs. The battery bar drops slowly and linear in this setting and if i measure the voltage, when the unit reports "Battery low" it is around 1,15V per cell. That also seems to be fine.


Would be worth to do the countercheck and use the NiMH setup for Alkaline batteries one time. :-)




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I have this same sort of issue with my Vista. (though i really dont care)


I'll put freshly charged NiMH batteries in, and the battery guage is full for about 30 minutes of use, then it drops rapidly (over 1 hour) to less than half power. Once it gets to this point, it slowly decreases to empty over about a 8 hour period of use.


This all has to do with the nature of rechargeables. Since their voltage is much less than alkalines, they tend to put out power very steadily and then drop off rapidly and suddenly when the juice is running out out.



Garmin Vista

Using Opera 7.1

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Alkaline batteries discharge linearly, starting at 1.5 volts and going dead at about 0.9 volts. This makes it very easy to monitor remaining capacity by using the voltage, e.g., if the voltage under load is 1.2 volts, the batteries are about half gone. NiMH batteries have a much different discharge voltage curve, starting at about 1.3 volts, dropping to about 1.2 volts within a few minutes of operation, discharging slowly from 1.2 down to 1.1 volts, and then going dead. Because the voltage is in the very small 1.1 to 1.2 volt range for most of the cycle, it is difficult to accurately monitor remaining capacity of NiMH cells by measuring voltage. But the main problem with using an alkaline gauge for NiMH cells is that the NiMH will rapidly go dead when the gauge shows 1/3 capacity remaining.




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