[pct-l] Bleeding off Lithium Batteries

[Liz Mares]

Thanks for this info...explains what happened to my camera batteries the other day!
   
  My GPS (eTrex Legend C) is supposed to use Alkaline or NiMH batteries but I know hikers have posted that they have used Lithium batteries in their GPS units without problems.  Has anyone tried it with this model?  Did you keep the Battery Type set to Alkaline in the system startup?  I don't want to wreck my GPS but it sure would be easier carrying just extra Lithium batteries.
   
  Thanks much!  ~~La Zorra~~ 

stewjohns at comcast.net wrote:
  I bought some new Lithium batteries for my Garmin GPS the other day, and when I put them in,
and turned on the unit, it came on for a few seconds and then the display faded out and the unit
turned off. The problem is that Lithium batteries come out of the box with a voltage of 1.8v, while
the equivalent alkaline battery has an out of the box voltage of 1.6v. The extra voltage of the 
Lithium, triggers the over voltage circuit in the GPS, and it shuts it off. The solution is to bleed off some of this voltage by running it through some other device for a bit. 

Being a curious electronic technician, I wanted to quantify this a bit and find out how much you 
need to bleed off before you can use them in the GPS. I pulled out my fluke multi-meter and measured the out of the box starting voltage of both alkaline and lithium batteries.
Alkaline = 1.6V
Lithium = 1.8 V

I then installed the New Lithium batteries in the GPS to verify that they would not work.
Then after confirming that they wouldn't, I installed them in a mini-mag flashlight. My plan was
to run the flashlight for 1 minute, measure the voltage of the battery, and than install them back in
the GPS to see if they worked. I intended to repeat this at 1 minute intervals until I could get
them to work in the GPS. My experiment lasted only 1 minute of data, as after 1 minute in 
the flashlight, the Lithiums worked fine. Measured voltage after the 1 minute bleed off---1.72V.
It doesn't take much bleed off to get them to work.

If you are a GPS user, and want to take
advantage of the extra life that Lithium batteries provide, I would suggest you test your spares
before you head out to the trail-head, and bleed them off a little if necessary. I suppose you could
rig something in the field if you had to, but why not be prepared ahead of time.

The GPS unit tested was a Garmin map 60CSX. The Batteries tested were Energizer Lithium AA,
and Duracell alkaline AA.

Doc Holiday
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