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Spent Batteries Are Still Good?

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Once my batteries get weak enough that they no longer work in my eTrex Legend, I had been throwing them away. One day I tried one of the used batteries in a toy and found that although they no longer had their full charge, they worked just fine in the toy. When my clock had a dead battery, I replaced it with one of the partially-spent batteries from my Legend and it seems to work fine now. (I wonder how long it will keep running on this battery that I would have pitched in the past.)


Could there be something wrong with my Legend that its battery power threshhold is higher than normal, or is this typical? If it is typical, I'll have lots of half-used AA's ready for use in other devices.



Edited by medoug
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Make sure that your battery type is properly set on your GPSr. There is a setting for different types of batteries and I think it is pretty much just for tracking the "juice" left in the battery and differs according to the set type. If it is set wrong it may well show the battery as being low on power when it really isn't.

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No, it can't be the setting alone since that just sets the battery power indicator level. These half-spent batteries are due to the low battery warning popping up on the screen and then followed by the Legend becoming completely inoperable (blank screen/automatically shuts off).



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As batteries die they lose voltage. The amplifier that the GPS uses to amplify the signal from the satellites would need a voltage over a certain amount. This is probably much higher then what you would need for a remote or whatever. (That is mostly a guess, but I do know that analog amplifiers need a bit of voltage)



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As Elracs says, some devices need a certain voltage to work and when the voltage delivered by the batteries goes under this limit, the device stops working. It only depends on this limit, which is lower for remote or a clock than for a GPSr or a digital camera.


Also, the main difference between alkaline and NiMH batteries is that when discharging, the alkaline battery will progressively drop voltage as NiHM batteries will keep a constant voltage and drop to 0V suddenly. See for example:Energizer Web Site.


That's why you have to "tell" your GPSr what type of batteries you are using so it can correctly predict how much charge is left. Example: Let's say that the battery life of your GPSr is 20 hours. If you set your GPSr to Alkaline and you actually put NiMH batteries in the unit, after 17 hours, it will still measure about 1.3V per battery and it will assume that the batteries are almost fresh. Then the unit will suddenly turn off without any notice.

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  Some devices are much more demanding on batteries than other devices.  Got a digital camera?  Try putting the “dead” batteries from that in your GPS.

Absolutely right. You can "cascade" your batteries to save money. Digital camera to GPS (still about 50% life), then to remote (or other low power consumption item) for many more hours of use.

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