The top power consumption I noticed was 19-20W during some background update tasks. Usually, it is in 4-6W range while working with documents, mail, surfing...
So, it could be possible to spend half the battery in one hour, theoretically...
It would be great if dock station has one more gadget: additional fan blowing quietly through SP3 when docked.
Then, we would have a real desktop when running in dock station (less or no throttling), laptop when taken away and notepad with separated cover. I wish... :)
During the update fan became active. After some time a thermometer icon appeared on the black screen and SP3 turned off. I waited a couple of minutes and powered on, update history shows all successful. We'll see...
Yes, I understand dockstation is connected via proprietary PCIe port with electronics to handle connectors, so mini Display and USB3 ports remain available on Surface.
"When Surface is locked, you can only use the pen’s top button. The eraser and right-click buttons won’t work until after you unlock Surface by signing in. When Surface is unlocked, all three buttons are available for use." (User Guide)
It depends also what you will store... I use SD for multimedia files and archives, so kept exFAT to exchange easier with others, the performance is good as declared, and I do not need much NTFS features like encryption, security policies etc.
I had a couple normal discharges, and after (I think) second firmware update it started to drop suddenly (at 30% or something)... not sure if that is related or a coincidence.
I use Samsung Micro SDXC Pro 64GB (up to: 90MB/s read, 80MB/s write): http://www.samsung.com/sg/consumer/memory-storage/memory-card/microsd-card/MB-MG64DA/APC
With large files it reached 84MB/s read and 68MB/s write, with many small ones it drops down to 10MB/s. I left exFAT format.