My 520 has no problems operating while charging, and will get right around 7 hours with the navigation running. With nav off, I can get ~12 hours with the typical 15-second backlight timeout. I carry one of those Anker 3300mah USB power sticks for rides I know are going to be especially long. I mean, the 520's battery is only something like 600mah, so I think it does remarkably well for a battery that size. with the Anker, I imagine 36+ hours with nav on wouldn't be an issue. The 1000 has a 1200mah battery, but also a significantly bigger screen-- and the two big battery killers are navigation and screen.

If you want absurd battery life, get something without nav or a color screen. I used a Bryton 310 for awhile, and after 24 hours of rides (a week and a half), the battery would be around 40%. I charged it twice a month.