810 has probably the best intrinsic battery life...
I did a 200 today and still had 40% battery remaining - rode just over 10 hours including stop for CAIK
It's pretty near the 17 hour claim..... (60% = 10 hours 90%=15 hours, 100% = 16.66 hours) YBLMV
I can top up its charge using a technet iep570 which allows at least 30 further hours operation, and it's a USB from the technet, and a garmin micro USB at the 810 end
Not sure what you mean by 'the position thing' but the original 'upload via iPhone and allow people to see where you are and your course etc' failed for me, largely cos the iPhone ran through its battery in a matter of five hours, and once the iPhone lost connection to its network all hell broke loose... It would not reconnect no matter what I did....
Mind you the screens are amazingly configurable, the number of screens available, ability to track power, heart rate etcetera is without peer....
It had some bugs early in the 2.9 firmware update, but all seems well now...
(I still run my 800 in parallel on the DIYxGPS rides, though, and it doesn't struggle over 400 kms now...)