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This is the GPS unit I got from Dawn Technology. I chose it because it allows the use of the remote at the same time as the GPS unit. Tested it last night and the 5m accuracy is accurate . Link:
http://www.dawntech.hk/di-GPS/pro_l_1.htm

I'm interested in something like this.

What sort of cost? Does it increase battery drain by much? How quick is it to pick up sats?

It cost me $300.00. I am not sure about the battery drain ( I have a few spares...). They say less than 36mA which seems little compared to the battery capacity.The acquisition of the first location is around tha 40s. It can record more than 260,000 data points. Have a look at their site, it seems to be among the better ones.

I use a Phottix Geo One, which drains my batteries like there is no tomorrow, but it just embeds into the EXIF so I don't have to worry.

Does this one embed? Please do share about battery drainage when you use it more!

glamy wrote:It can record more than 260,000 data points.

I'm a bit confused about this point: with the Nikon bodies the point about connecting to the body is that the GPS supplies data to the body in NMEA format (which apparently this one does) so the body embeds the GPS data into each photo as it's taken.

What does this unit need to record/store data points for?
Not that it might not be useful to have a trail recorded of your travels (not just at the instants you took photos). I use a GPS logger that can record for almost 2 weeks at 10s intervals, and use that to attach locations to photos based on timestamps, but that particular use is made irrelevant here (unless you decided to use that data for images from the other cameras you were using at the time - you might not have a separate GPS for every camera).

DaveB wrote:What does this unit need to record/store data points for? ... it might ... be useful to have a trail recorded of your travels

Except that the only interface appears to be to 10 pin Nikon connector, so there is no way to actually read the track log. Unless of course you have a Nikon-USB converter lying around. Do they even exist?
I suspect it was simply built into the chipset they used so they made it a "feature" even though it cannot be accessed.
"Caveat Emptor" springs to mind

As for the battery life, my EN-EL3e claims 1500mAh. That means you will drain the battery in less than two days (41.67 hours) even if you don't use the camera. Much less of course if you do. Definitely something to use at need, not leave on the camera.

This unit does embed the data in the Exif. It also can be used to map your travel. It connects to a computer via a USB adaptor that is supplied with the unit, the sofware to do the mapping is also free. The data in the Exif can be found in the Xmp file of Photoshop and copied straight into Google Earth to get to the location. Here is a link to a picture
I have taken this morning. Under the picture is the option "view map" that takes you to the spot:
http://www.pbase.com/glamy/image/126176618
A picture of the configuration to connect to a computer:

Mr Darcy wrote:As for the battery life, my EN-EL3e claims 1500mAh. That means you will drain the battery in less than two days (41.67 hours) even if you don't use the camera. Much less of course if you do.

Actually Greg, it's not that simple. Power == Volts * Amps

Your EN-EL3e runs at 7.4V (?) whereas I don't know off the top of my head what voltage the GPS is running at. If it's 5V then that would mean your number is off by 1.5* (>61.5 hours).

DaveB wrote:

Mr Darcy wrote:As for the battery life, my EN-EL3e claims 1500mAh. That means you will drain the battery in less than two days (41.67 hours) even if you don't use the camera. Much less of course if you do.

Actually Greg, it's not that simple. Power == Volts * Amps

Your EN-EL3e runs at 7.4V (?) whereas I don't know off the top of my head what voltage the GPS is running at. If it's 5V then that would mean your number is off by 1.5* (>61.5 hours).

Dave,
You are right,it does run at 5V and the EN-EL4a is 2500mAh @11.1V, should last a while. I think most of the drain will be using live view.

DaveB wrote:

Mr Darcy wrote:As for the battery life, my EN-EL3e claims 1500mAh. That means you will drain the battery in less than two days (41.67 hours) even if you don't use the camera. Much less of course if you do.

Actually Greg, it's not that simple. Power == Volts * Amps

Your EN-EL3e runs at 7.4V (?) whereas I don't know off the top of my head what voltage the GPS is running at. If it's 5V then that would mean your number is off by 1.5* (>61.5 hours).

Um no Dave I'm not.
The unit clams to draw 36 milliAMPS The batttery supplies 1500 milli AMP hours. Power does not enter the equation.
The battery will supply 1500 milli amps for one hour. Or 36 milliamps for 41.67 hours

Amp hours is a measure of energy, not power.
Current times time = energy

However it does say "less than 36mA" so that is a worst case scenario. Also glamy is using a 2500mAh battery. That WILL change the equation.

Based on my GPSr, energy usage is highest when it is looking for satellites. Once it has found them it will use less energy. Just a burst now and then to maintain signal

Glad to see that the device comes with a USB to Nikon converter. Could be handy for other things.

Mr Darcy wrote:

DaveB wrote:Actually Greg, it's not that simple. Power == Volts * Amps

Your EN-EL3e runs at 7.4V (?) whereas I don't know off the top of my head what voltage the GPS is running at. If it's 5V then that would mean your number is off by 1.5* (>61.5 hours).

Um no Dave I'm not.
The unit clams to draw 36 milliAMPS The batttery supplies 1500 milli AMP hours. Power does not enter the equation.
The battery will supply 1500 milli amps for one hour. Or 36 milliamps for 41.67 hours

Amp hours is a measure of energy, not power.
Current times time = energy

Sorry: if something draws 36 mA at 5V, then (given a 100%-efficient voltage converter!) that would equate to 24 mA coming from a 7.4V supply. The device is drawing 36 mA at 5V because it's consuming 0.18W of power.
Of course, there's no such thing as a 100%-efficient voltage converter...

Amp-hours is not a measure of energy by itself. A 1500 mAh 7.4V battery contains a lot more stored energy than a 1500 mAh 1.2V AA!
In fact, four 2600 mAh 1.2V NiMH cells together has less capacity than a single 1800 mAh 7.2V Li-Ion battery!

aim54x wrote:I use a Phottix Geo One, which drains my batteries like there is no tomorrow, but it just embeds into the EXIF so I don't have to worry.

Does this one embed? Please do share about battery drainage when you use it more!

A bit of a late answer... During the trip I had with Paul in August I had to charge the D3s every day (10 hours) if I did not want to swap batteries the next day, that is having the GPS on all the time. The D2x could go on for days with a slightly lighter usage. So the GPS does drain the battery fairly fast...
It doe embed in the exif.
Cheers,
Gerard

Good to see that I do get an answer in the end....draining a D3s to the point of a daily charge being required means your in the same boat as me.....oh well