Pros: Beautifully designed and built. From the perforated look rubberized area where your thumb rests to the brushed metal strips which arcs gracefully around the side of the mouse, to the low gloss plastic finish and the metal scroller wheel with rubber insert, it's a beautiful mouse, high quality mouse.It's extremely comfortable as well. Perhaps not quite as much as my old MX Revolution, but very close.Darkfield is extremely precise and works on every surface I've tried, from my shirt to my glass desk.This is the Cadillac CTS-V of mice.Battery is a removable and replaceable AA unit, a nice feature since internal battery failure caused the death of my MX Revolution.Charging is done via USB cable, so no down time.Battery life on its first full day of use is excellent, still 3 bars after hours of use.Have a middle mouse button again! Now shifting between the wheel modes is done via dedicated button.Nifty little travel casePlenty of programmablity.Cons: Cons are only a few.Forward/back/zoom buttons don't quite fall into reach as naturally as they did on the MX Revolution.Loss of shift-to-click. I'll miss this feature. Loved how the MX Revolution could be programed to switch from geared to free spin depending on how fast the wheel spun, then would switch back.Other Thoughts: My dear MX Revolution bit the dust on me a few weeks ago, due to internal battery failure, yet despite buying the original four years ago, Logitech replaced it with the new model.It's really worth saying that their customer support is superb, friendly, and helpful. They also send you return shipping labels now so you don't have to pay for shipping. Now that's progress. Turnaround was about 2 weeks total. I will continue to buy products from Logitech, they stand behind them.My only other minor complaint is the Application Switcher. I don't care for it...distorts the windows and when many are up it looks cluttered. But that's just a keystroke assignment away to set it back to Document Flip, so it's not an issue.Overall I love this mouse so far, and while I do miss my MX Revolution, this is a worthy successor. It's even better looking and very nearly as comfortable, very precise and works on surfaces the old mouse never could.Hopefully it will last! 

Question: Where is battery ?
Answer: Battery is a removable and replaceable AA unit