LEL 2013 / London - Edinburgh - London Audax

My Garmin 800 with the Garmin Powermonkey pack only lasted 23.25 hours.
If you can get a power source that lasts then you might want to force it to save each 12 hours or something by doing a reset - some people report Garmins dying on long rides.

Mine died on Sunday after 16 hours. I had to remove the memory card to get a PC to even recognise it (even though the ride wasn't on the card) and managed to get 90% of the ride data off it that way (it also needed fixing via an online tool). Then I had to do a factory reset to get the unit to power back up (even though it still had 91% battery as it had been running from a powermonkey).

I had recently updated the firmware to 2.5. I had no such problems on 2.4 - but I had very similar experiences with 2.2 in the past. Make of that what you will...