Garmin etrex - how much does wrong battery type change the accuracy?

[mzjo]

As some may be aware I have been having accuracy problems with the distance and time displays of my eTrex 20x (like showing 3x real distance and impossibly short moving time) which makes the trip computer really useless. Recently I have been using rechargeables rather than alkalines (can't be bothered to go out and buy batteries!) which might coincide with the problems (can't be absolutely sure since I don't keep records but probably the case). On sunday I took the garmin with me walking the dog. Usual thing reset everything to clear the trip display, which means resetting to factory defaults. Usual highly improbable time and distance displayed but at half-distance I looked at the system details and lo and behold battery type alkaline. I know that I had changed the setting to rechargeable - but before clearing the trip settings! I did then correct the battery setting (at the half distance stage) but didn't reset the trip, just remembered the times. At the end it looks like this improved the accuracy (although moving time with a dog sniffing all the smells might be expected to be a bit hit or miss; total time appeared to be closer to right).

So the idiot's question (before I am tempted to presuade the garmin to do the sensible thing and fall off under a bus!): does having the wrong battery type really throw the device to that extent? If so, why isn't it capable of detecting battery type or removing battery type from the factory default reset? And what is the trick for resetting the trip computer without going through resetting all settings? (I ask this because when I try just clearing trip data I seem to always have some residual data that remains).

With that sorted I might have another go at actually following a track. RWGPS has all sorts of advice for doing that so I might eventually succeed but after two years occasional use a wired cycle counter and a map are still more use to me!

[Cudzoziemiec]

If the eTrex 20x works in the same way as the 20 – though it sounds like it might not – then you can reset the trip recordings by simply going to Track Manager > Current Track > Clear Current Track. This resets the various time, distance and average speed readings – though not maximum speed – to zero.

[Kim]

I can't imagine how the battery type would cause that sort of inaccuracy.  AIUI all the the battery type setting does is change the calibration of the battery gauge and the threshold for the 'battery low' warning.

It can't determine the battery chemistry automatically, because all it can do is measure voltage.  It has no way to know if a battery that's producing 1.3V/cell is a full NiMH or a partially depleted alkaline.  (I've occasionally thought that AA cells would benefit from a conductive pattern like they use on 35mm film cartridges to tell the camera the ISO rating.)

[JonBuoy]

As I understand it the battery type needs to be set to ensure that the battery gauge is properly calibrated.  Other than that it has no effect on the functioning of the unit.

[Lightning Phil]

There are two odometers on the 20x. One is a trip odometer and one seems to be a lifetime one.  Do you have your trip computer field set to the lifetime odometer? Thus you need a factory reset to reset it.

When on trip computer page it should be. Menu button on left, click first option with clicker, and confirm clear.  That’s what I do on my eTrex 30x and no probs with funny distances.

I can’t imagine wrong battery setting would cause your problems.

[mzjo]

If the eTrex 20x works in the same way as the 20 – though it sounds like it might not – then you can reset the trip recordings by simply going to Track Manager > Current Track > Clear Current Track. This resets the various time, distance and average speed readings – though not maximum speed – to zero.

Yes this happens and it doesn't change battery type.

There are two odometers on the 20x. One is a trip odometer and one seems to be a lifetime one.  Do you have your trip computer field set to the lifetime odometer? Thus you need a factory reset to reset it.

When on trip computer page it should be. Menu button on left, click first option with clicker, and confirm clear.  That’s what I do on my eTrex 30x and no probs with funny distances.

I can’t imagine wrong battery setting would cause your problems.

Doing this brings me to the same page as reset in the system menu (which is where I was going before). On my 20x clearing the first item changes the battery type!
How do you know (=where do you find) the odometer setting to reset the field (and how do you reset it)?

Next step will be do some recording and post a photo of the screen if there is an anomaly. I'll keep working on it for now but there is no shortage of buses in Limoges if need be.

Forgot to say thank you all for all the help, it really is appreciated

[Cudzoziemiec]

It sounds to me as if there must be some weird misconnections between what you're clicking on screen and what actually happens. But I can't see how any of that would affect accuracy in itself. Has it always been like this or is this a fault which developed after some time?

[mzjo]

It sounds to me as if there must be some weird misconnections between what you're clicking on screen and what actually happens. But I can't see how any of that would affect accuracy in itself. Has it always been like this or is this a fault which developed after some time?

I will try it out again on sunday and try to think of taking photos of the screen if (when?) it misbehaves. It has always been a bit iffy (like adding the distance from home when you thought you had cleared everything; when home is in France and you're in England, as one might imagine, this gives wildly improbable average speeds, way over the indicated max speed. It also has a habit of drawing filthy great straight lines between points on the map where it was meant to be switched off; I currently have one that I can't seem to get rid of!). I have always assumed that this sort of behaviour was due to my being inept in Garmin management.
Sometimes it works properly but I can't make it repeat this at will!

Anyway we will see on sunday. Perhaps I won't have anything to show 

[Feanor]

Just thinking out loud...

After you switch the unit on after either a significant change of position, or a significant period of time, it can take the device a minute or two with a good sky view to get a fix.
You need to wait till it's got a correct fix before starting to record a ride, or there's the risk it might use it's last-known fix as the first point in the new tracklog.

Is that a possibility?

[Kim]

It sounds to me as if there must be some weird misconnections between what you're clicking on screen and what actually happens. But I can't see how any of that would affect accuracy in itself. Has it always been like this or is this a fault which developed after some time?

I will try it out again on sunday and try to think of taking photos of the screen if (when?) it misbehaves. It has always been a bit iffy (like adding the distance from home when you thought you had cleared everything; when home is in France and you're in England, as one might imagine, this gives wildly improbable average speeds, way over the indicated max speed. It also has a habit of drawing filthy great straight lines between points on the map where it was meant to be switched off; I currently have one that I can't seem to get rid of!). I have always assumed that this sort of behaviour was due to my being inept in Garmin management.

This is a known 'feature' of the new (ie. post-HCx) eTrexen:  It saves the last known location, and on startup will - for reasons that can only be explained as sloppy programming - record this as the first trackpoint before it starts logging new GPS data.

The work-around is to wait until it has a GPS fix before you clear the track / reset the trip computer at the start of a ride.  (On the HCx and before, you could clear the track while you were waiting for the GPS to get a fix, and it would do the reasonable thing and start recording from wherever it was when it got a fix.)

[Pingu]

...wait until it has a GPS fix before you clear the track / reset the trip computer at the start of a ride...

This.

[IanDG]

...wait until it has a GPS fix before you clear the track / reset the trip computer at the start of a ride...

This.

Yes, I had issues with distance travelled on an audax because i reset too quickly. Wrong battery types just tells you that you have no power left prematurely

[mzjo]

It sounds to me as if there must be some weird misconnections between what you're clicking on screen and what actually happens. But I can't see how any of that would affect accuracy in itself. Has it always been like this or is this a fault which developed after some time?

I will try it out again on sunday and try to think of taking photos of the screen if (when?) it misbehaves. It has always been a bit iffy (like adding the distance from home when you thought you had cleared everything; when home is in France and you're in England, as one might imagine, this gives wildly improbable average speeds, way over the indicated max speed. It also has a habit of drawing filthy great straight lines between points on the map where it was meant to be switched off; I currently have one that I can't seem to get rid of!). I have always assumed that this sort of behaviour was due to my being inept in Garmin management.

This is a known 'feature' of the new (ie. post-HCx) eTrexen:  It saves the last known location, and on startup will - for reasons that can only be explained as sloppy programming - record this as the first trackpoint before it starts logging new GPS data.

The work-around is to wait until it has a GPS fix before you clear the track / reset the trip computer at the start of a ride.  (On the HCx and before, you could clear the track while you were waiting for the GPS to get a fix, and it would do the reasonable thing and start recording from wherever it was when it got a fix.)

Just thinking out loud...

After you switch the unit on after either a significant change of position, or a significant period of time, it can take the device a minute or two with a good sky view to get a fix.
You need to wait till it's got a correct fix before starting to record a ride, or there's the risk it might use it's last-known fix as the first point in the new tracklog.

Is that a possibility?

That sounds like operator idiocy which for some bizarre reason I find much more acceptable as an explanation than machine malfunction. It must be that human error is a more common reason for equipment failure. I will try and see what happens tomorrow!

[mzjo]

It Worked!!!!! I haven't looked at the map trace yet (although that usually works so I wouldn't expect a problem) but this bit with distances and times worked just fine.

So thank you Kim, Cudzo, JB, Phil, Feanor and Ian (and anyone else I might have missed out), that might look to be nothing to you experts but it's a quantum leap forward for me!!

now another little question: is there much point in selecting GPS +Glasnos satellites if there is a good fix (today I had 4 full strength GPS satellites + 2 others and what I presume is the accuracy at 7m so I didn't bother with the russians)? Does the unit use more power handling the extra satellites?

[Kim]

now another little question: is there much point in selecting GPS +Glasnos satellites if there is a good fix (today I had 4 full strength GPS satellites + 2 others and what I presume is the accuracy at 7m so I didn't bother with the russians)? Does the unit use more power handling the extra satellites?

The benefit is mostly when you have a restricted view of the sky, as more total satellites mean more will be within view.  So it's useful in urban areas, on the side of mountains and similar.

But yes, it does use a little bit more power for GLONASS+GPS.

[frankly frankie]

You can get your Etrex to save screen dumps.  E.g,



I happen to think the Glonass is largely cosmetic, not convinced it actually does anything at all.  I'd be more impressed if there was an option for 'Glonass only' but there isn't on mine.

[Lightning Phil]

I just leave it on gps but I don’t generally ride in terrain challenging for GPS. If I was riding across London Glonass might prove useful, though I tend to use rough and ready reckoning for there.