Power source

[Androcles]

I've been thinking for a while about getting a GPS, nothing fancy really, just something to take the place of the paper routesheet for audaxing was what I had in mind.  I have an old Windows phone (MDA) which I use occasionally in the car as it has TomTom and I wondered whether I could press that into cycling service.  After a bit of Googling I found an app called GPS Cycling Computer which, much to my pleasant surprise, installed on the device and seemed to work.  I also managed to download a swathe of map tiles from OSM and import a gpx track-to-follow.  So far so good.

I know that the Achilles Heel of a phone based solution is the battery life.  The MDA runs TomTom for about 3 hours with the screen on full time and that's going to be barely enough for the Wednesday pub ride let alone an overnight audax (which is really what I want it for).  As far as I can see my options are to run the thing of an external battery pack or the dynohub.  I've found this http://www.ebay.co.uk/itm/Mini-12000mAh-2-USB-External-backup-Battery-Power-Bank-Pack-for-iPhone-iPad-HTC-/150947015111?pt=LH_DefaultDomain_3&hash=item232524a9c7&_uhb=1 which, on the face of it, looks just the job - am I being hopelessly naive to assume that a 12000mAh external pack will extend the life of a 1200mAh internal battery by 10 times?  Should I look at powering the device off the dynohub?

I've got a feeling that this will go the way of all of my homemade lash-ups and I'll end up with a Garmin in the end, but in the meantime it will be an interesting winter project - which is sort of the point really.

[Feanor]

External battery packs do give such devices usefull run-times.

I don't know about your particular device, but I can say this:
A garmin edge 800 is good for 10 hours, 14 at a push ( no navigating or using the backlight ).
With a TeckNet 11000mAh pack, it lasted the 36 hours of a 600k, and the battery pack was still on 3 out of 3 LEDs for charge.

Dunno what the battery drain of your device is, but the the external batteries do work.
I'd suck it and see.

R

[fhills]

How much would that external battery solution cost?

And anything with an external battery is surely more complicated/faff/

The Etrex 20 I think will run for 24 hours (a lot of cycling) on a single pair of rechargeable AAs and you can of course carry spares.

[Androcles]

The external power pack is listed at 22 quid.  I'm trying to use as much of my existing hardware as I can.  As I say, I may well end up with an Etrex (particularly if I can get one second hand) but I'm not ready to take that plunge yet, and if/when I do the external will still be useful as a backup for my phone.