I use an 801 with USB pass-through (5v) at my desk. Battery Life: Infinite!
The 801 holds a boat load of juice, and at 5v, produces tons of vapor.
At work, I use a Titan "Mega". (which is a 510 with a bigger battery). it is pen-sized, so it's invisible next to pen in my top pocket. The "mega" battery lasts a long time. I can't vape heavily at work, so it easily lasts me a full work day, but I do bring a spare, just in case.
Out socially (shopping, movies, out to dinner, etc) I use a standard 510 as it's smaller and sleeker and easy to "palm" the device without drawing attention. Yes, it's a smaller battery and won't last as long, but given it's size, ther performance has been terrific.
I'm interested enough to purchase a "Tornado" from TotallyWicked (or the Janty Ego, same thing) when I catch a sale. But right now, I never find myself short on battery power, so I never feel a real "need" for it. I just like the way it looks, and have plenty 510 attys to attach to it.
A note on atty's and voltages: Higher voltage means hotter elements. Be aware that "Hotter" elements will change the flavor of your vape. I find this to be true. The 510 atty has a reputation for this, as they always run a bit "hot" (hence, the vapor). My 510's do tend to "break the flavor down" just a bit. I'm always suprised at the flavor difference between the 801 and 510.
(definately love them both, though.)
Side Note: I only rarely carry the 801 around with battery, as it is fairly large, and it WILL leak a boat-load of juice if it gets inverted. I'll stick it in a top pocket (mouth-piece DOWN) when outside, working around the house, or sometimes in the car, as I have a USB car adapter to run it from so I'm not eating up batteries while driving.
Hope that helps.
-berk