GPS Battery life

[Genghis the Engineer]

I'm proud owner of the following:-

(1) A handheld GPS
(2) A battery tester
(3) A magic machine which recharges normal batteries.

Through use of these, and occasionally other people's GPS units, I've come to realise that at the point when most (not necessarily all - Garmins seem to be about the worst however) handheld GPS units say the batteries are flat and turn themselves off, the batteries are generally still at about 75% charge. Quite why this is I'm unsure, my best guess being that GPS units often rely upon having a peak voltage to run.

The moral is that (a) if you own a magic battery recharger (which work fine so long as the batteries aren't too far discharged) you can save yourself a fortune in Duracells, and (b) even if you don't you can run torches, etc. quite happily from the batteries that your GPS has just told you were flat.

It also goes some way to explaining why some GPS units seem to literally "eat" batteries.

Just a bit of acquired wisdom I thought I'd share.

G

[28thJuly2001]

You don't get much warning with the GPS Pilot either,
"WARNING....LOW BATTERY LEVEL" followed 5 minutes later by a blank screen.

Walt,,

[bluskis]

I have managed to extend the life of my batteries tenfold in my Pilot 3.

I simply take out one of the cells when the GPS is not in use. Prior to this, and unknown to me, the 'on' button was easily depressed by movement or other pressure while in my flight bag, consequently gobbling up battery life.

I am guessing that I now get about 30-50 flight hours out of a set of batteries, as they are only used to set up the flight plan, the aircraft electrical system providing most of the remaining power requirement.

[dublinpilot]

Genghis,

I'm guessing here, but another problem you might be having, is that re-chargable batteries generally work on 1.2v, while non-rechargable ones are 1.5v.

If the garmen is checking the voltgage, then fully re-charged batteries, will probably seem fairly well used to it, as it's already down .3v

Only a guess, but I'd think I'm not too far from the mark with it.

[Genghis the Engineer]

No, I'm talking about normal 1.5V alkaline batteries, rechargeables rarely work at-all in a GPS. You can buy chargers, costing around £30-£40 which recharge these (generally if completely drained, they won't, but a 50% drained battery recharges up to about 95%).

G

[Fujiflyer]

Genghis,

Be careful that the batteries don't begin to leak - I tried to charge some a while back (D size, Duracell) using the correct type of charger however they had been run too flat and ended up leaking alkali (KOH, I think). dublinpilot had a fair point - I have witnessed the same thing myself however obviously this is not the case in your situation. As bluskis implies, with many battery powered devices there is a "quiescant consumption" of power, ie whatever it is (the device) draws a small current all the time, usually to maintain some bit of circuitry within (for the keypad, etc). My GPS (a Garmin) is fine in this respect but I have some other equipment which is a right pain for wasting batteries.

[Genghis the Engineer]

As I indicated, the charger's instructions are clear that recharching completely discharged batteries doesn't work. In the case of my device, it flashes a warning light at me and refuses to do anything - presumably for the reason you say.

G

[Lowtimer]

Ghengis,

If you are having trouble with "proper" rechargeables, perhaps you are using the wrong ones. The 500 mA/h AA nicads I used in my mis-spent youth with radio controlled models are pretty old tech now. I have some extremely ordinary (Argos catalogue) NiMH AA cells which I have used as two sets of four in a variety of Garmin GPS handhelds over the last two years and rarely get less than six hours use out of a freshly-charged set. These batteries, rated 1200mA/h, are no longer state of the art, and industrial cells (Sanyo, Ansmann etc) of 1800mA/h or 2000 mA/h are now becoming quite widely available. I also have a pair of the Ansmann PP3 shape NiMH 9v batteries that I use alternately in to my aftermarket ANR headset conversion, these are only 160 mA/h. One of them recently ran the headset happily for 8 hours of Yak flying over two days, and the Yak drains the battery much more than a quieter PA-28 style environment. One thing you do have to watch with NiMH, though, is that the batteries do have to be _freshly_ charged, as they will self-discharge over a couple of weeks. For that reason it's a good idea to have a discharger which will run them down so you can recharge the night before flying, or invest in a decent micro-processor controlled charger.

There are a couple of web sites where these cells can be obtained. I don't want to breach the PPRUNE rules by posting a commercial link but specialist photographic suppliers often carry them and a web search on Google UK using the terms "NiMH" and "battery" will usually do the trick.

[drauk]

Following on from lowtimer's comments, one can indeed use NiMH rechargeable batteries in Garmin hand-held GPS units.

The Pilot III (for example) includes a menu option to tell the unit that you are using rechargeable batteries, presumably so that it knows to expect 1.2V, rather than 1.5V it would get from an alkaline cell and give "low battery" warnings accordingly.

Given that a charger and 4 AA NiMH 1800mA/H cells is available so cheaply I personally wouldn't bother with an alkaline battery charger.

Also note that depending on the sophistication of your battery tester, it may not give particularly accurate readings. Inexpensive battery testers don't place the battery under any load and this gives misleading results.

[Genghis the Engineer]

Actually I have a supply of cheap Duracell equivalents, supplement by recharging real Duracells that everybody else throws away from their Garmins (my Magellan doesn't seem to suffer the same problem). Mostly I just wanted to make the point for other peoples benefit - I don't really have a problem.

G