Can Garmin Edge 500/510 and 800/810 be charged while riding? Extended battery life is very neccesary for using the device on long brevets and multi-day endurance racing.  Can Garmin Edge cycling GPS units 500/510 and 800/810 be charged while riding via external battery pack like or USB dynamo charger? 

Can you plug in while riding?  Are only certain devices able to charge the unit while it's recording / navigating?
Just verified that the 510 can be attached to power while on/in use. It continues to operate. When the external power source is removed, it will give a message to that effect, but does not power down (like the nuvi/car versions do).

Note that you (obviously) have to open the weather seal to plug in power.

Also worth noting, the 510 will go into a different mode when you plug it into a computer. Unsure if it will continue to record, but the screen shows the computer attached so suspect not.

For long trips like you describe, a device like these http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&amp;field-keywords=phone+battery+backup
should do the trick.