Battery Life

Dear List,

on the subject of "battery life" I read on www.garmin.com

- eTrex Legend®: 18 hours
- GPSMAP® 60CSx: 18 hours, typical
- eTrex Vista® HCx: 25 hours
- Colorado 300: 15 hours

what kind of use could be sustained during this time?
- tracking sats and saving tracklog?
- tracking sats, saving tracklog and drawing/updating maps?
- tracking sats, saving tracklog and drawing/updating maps w/ light on?

a rather OT question: what's the capacity (in mAh) of a regular Duracell
alkaline AA battery?

[]s,

--

Having the backlight on will significantly decrease the battery life.
The exact amount will vary by model, but I've found around a 30 - 50%
reduction (or even more with models that have multiple brightness
levels). You can get about a 40% increase in life by turning off the
radio receiver circuits (i.e. using demo/simulation/GPS Off
operation). Of course it can't do any tracking in that state, but you
can still look at the maps, find POI locations, examine your tracklog,
etc. Most Garmin also allow you to operate in 'Battery Saver' mode
where the radio circuits are turned off for periods of up to 5 seconds
as long as reception is good and you're moving predictably.

The other functions mentioned won't have much of an effect, at least
in 'Normal' mode. In 'Battery Saver' mode the power usage goes up if
reception is bad and will approach the lvel you get in 'Normal' mode
if you have either really bad reception or you're moving fast and
unpredictably (always changing direction and/or speed).


AIRC, the nominal rating of good alkaline AAs is about 2900 mA-hr.
But note that this is tested at very low current levels (around 20 mA)
and alkalines have much less effective capacity as the current drain
increases due to their high internal resistance reducing efficiency
(that's why they're so bad in many digital cameras). At typical
current drains found in GPS receivers (100 - 200 mA range) the
effective capacity drops to around 2000 - 2500 mA-hr. And in digital
cameras which may have a current drain of 1000 mA the effective
capacity of alkaline cells is only about 800 mA-hr.

Lithium, NiMH, and NiCd cells retain their nominal capacity much
better at high current drains.