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Living with a Garmin:

Battery Runtime and Etrex Jitter

Urban myth: portable 'leisure' GPS devices are too battery-hungry to be useful.

Newer units are much improved in this respect over older models, and at the same time, batteries themselves have improved. According to Garmins own specs, the run-time king is the Etrex Legend or Venture C or Cx series (NB the Legend and Venture are exactly the same hardware, apart from the colour of the case). They quote 'up to 36 hours' battery life for the Legend C, which uses 2x AA cells, and 'up to 32 hours' for the Cx.

Other Garmins either use smaller cells (Geko) or are rechargable-only (Edge) or have onboard compass and barometer (Vista) or use older less efficient circuitry (Etrex mono models) or use a more sensitive receiver (Etrex H series, or the 60 or 76 or Colorado or Oregon or Dakota models) or a bigger or brighter screen (60/76/Colorado/Oregon). All these things make for shorter runtime, though its not always a serious hit - I wouldn't let runtime alone put me off buying an H or a 60 or a Vista. The new Colorado/Oregon series do look a bit problematic though, for runtime - the touchscreen interface doesn't help, nor does the more powerful processor in use.
(Scroll down to see some current drain figures from user tests.)

Some people report that running the GPS with the map page active (the map is continually scrolling and the display upodating itself) uses more battery than leaving it on the trip computer page, or the compass page. Again I don't think it's a big difference and I wouldn't let it deter me from using the map page.

A good pair of NiMH AA cells, freshly charged, will easily run a Legend/Vista Cx for 24 hours non-stop, on the map page, including using screen backlight and warning tones. That seems to me to be good enough, really. To get round a 600km, you could take one of several options:
* only turn the GPS on when you need it. (OK, that's a bit extreme!)
* change the battery at around half time, buying new alkalines from a garage or carrying a spare set with you.
* run the GPS in 'battery save' mode.
* fit a pair of Energizer Lithiums and run the GPS in 'alkaline' battery mode.

Lithiums is an excellent option. Sheila did this for PBP and she was halfway back to Paris before the first pair of lithiums ran down - a runtime of maybe 50 hours. Lithiums have another virtue - they are very lightweight, so help to reduce the possibility of 'Etrex Jitter', of which see more below.

Battery Save Mode works pretty well - I've used it a lot on the Geko because, with that unit, run time is a problem and battery changing by the roadside a bit of a pain. Battery Save reduces the frequency at which the satellites are polled - from about 1 second intervals down to about 5 seconds I believe. I don't really notice any difference in performance, in real-world riding situations. You might notice it if you tested for it, by riding round a tight roundabout or something with your eyes glued to the screen - but in practice its completely usable. On the Geko it seems to extend battery life by about 20-30% - just enough to make a good pair of NiMH AAAs last all day.
Incidentally, enabling WAAS would also be a slight battery hit - and the increased accuracy (from EGNOS, in Europe) hardly seems necessary for cyclists' purposes.
Likewise, on the very new units that can receive the GLONASS or Russian satellites - you can turn this option off for slightly improved runtime without really any loss of perfrmance.

If carrying spare cells for GPS (or lights) in your luggage or pocket - get hold of one of these plastic containers to keep things neat and safe and free from short-circuits. They come in 2x, 4x or bigger, and various sizes to suit AA, AAA or CR123.

If carrying spare cells, Energizer Lithiums are ideal - they have a very long storage life, weigh less than other cells, and pack lots of punch. That tiny pair on the left could stay in your pack for years, you won't know they're there, and they'll still work when you need them.

Etrex Jitter is when a bit of vibration causes the GPS to turn itself off. Its caused by a momentary loss of power to the circuit board. There is a spring-loaded contact between the battery compartment and the board itself.
It is not the sprung battery contacts, which are a good tight fit - this is a common misconception but the offending contact is deeper inside the casing, and, crucially, inside the fully-waterproofed section, making it difficult to do an easy fix.
As the GPS ages, the problem does seem to get a bit worse.
Use of NiMH batteries, which are 30% heavier than alkalines and twice the weight of lithiums, probably doesn't help, because of their increased 'battering ram' effect when the GPS is vibrated.

Although often ascribed to Etrexes, the problem, and the root cause of the problem, is common to all Garmins that run off 2x AAs.
'New' Garmins that use the new-style 'spine' mount, are less prone, simply because the mount is much better.

* There is no easy fix that is 100% effective, other than returning the unit to Garmin.

* A very easy fix that is 90% effective, is to eliminate any rattle in the mounting system.
Simply add 2 or 3 layers of PVC tape to the mounting foot (on the back of the GPS case) to make it a tighter fit on the Garmin handlebar mount. Take care not to interfere with the latch, and also make sure the slotted screw head is good and tight before covering it with tape.
Or use the RAM Etrex Cradle which is a solid 'alternative' mounting system - beefy, still quick-releasable, but much bulkier.
GPS Warehouse offer the RAM Etrex Cradle (RAM-HOL-GA16 for colour models or RAM-HOL-GA5 for older ones) which fits on their Rail Mount (RAP-274).
* If you prefer the neater Garmin mount (as I do) then always opt for the oversize version. On ordinary (non-oversize) handlebars this requires more rubber sleeving so adds a bit of compliance - this helps a little bit with beating the jitters, though not as much as adding the PVC tape does. The oversize mount is more practical in other ways too.
* Also remember that Lithium cells are half the weight of NiMHs - reducing the overall weight of the GPS - I find this helps a little bit as well.

** The ultimate fix is to add a small electrolytic capacitor across the power rail which will smooth any short interruptions in power supply.
22uF should be enough. To be really effective this needs to be done on the circuit board itself (ie, not just across the terminals in the battery compartment). Or just hard-wire the battery compartment to the circuit board. Either way, this means opening the case - probably the GPS will never be waterproof again, afterwards. But if you want to try it, here are three illustrated pages which show the way:
the instructions are here
and here
and here
and here (external link)

Francis Cooke

Appendix: These battery drain figures are from www.gpsinformation.net/main/bat-5.txt

GARMIN UNITS WITH TWO AA BATTERIES
Internally Powered with Fresh Alkaline Batteries
--------------------------------------------------------
                        (Test Mode)     Antenna Connected
Model       Version     Sim  Searching    GA27C or GA26C
--------------------------------------------------------
eMap           2.04     60ma  120ma     130ma      NA
Legend         2.30     50ma  120ma       @        @
Vista          2.16     50ma  120ma*      @        @
  *165ma with compass ON
Vista C        2.10     52ma   62ma*      @        @
  *100ma with compass ON
Vista Cx       2.20     50ma   65ma*      @        @
  *75ma with compass ON
GPSMap 60CS    3.50     38ma   71ma#    Gilsson: 82ma
  #Backlight low: add 23ma
  #Backlight med: add 44ma
  #Backlight max: add 100ma
  #Compass ON: add 40ma
GPSmap 76      2.04     62ma  120ma     130ma      NA
GPSmap 76S     1.06    100ma  125ma*    185ma      NA
  *Compass ON: add 50ma
GPSmap 76C     3.43     52ma   62ma*     70ma      NA
  *With backlight full: add 100ma
GPSmap 76CS             55ma   62ma*
  *With backlight: 20% add 25ma, 30% 33ma, 50% 53ma, 100% 103ma
  *Compass ON: add 35ma, Tone: add 70ma (Approx)
GPSmap 76Cx    2.40     40ma  100ma*
  *With backlight full: add 100ma
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* Searching
° On Garmin models, the lower the battery voltage, the higher the current drain.