Wireless trackballs should be pretty good on battery life. The Logitech M570 claims that it can run for 3 years on one battery. I've had mine for about a year now and the battery it came with is still good.
Not sure what you mean by minimalist, but here's the more common options:
Kensington Slimblade: 4 buttons, scroll by twisting ball, $80
CST L-Trac X: 3 buttons, flywheel, can add custom buttons, $160
Logitech M570 Wireless: 5 buttons, wireless, right-handed only, thumb ball rather than finger ball (these are harder to be precise with), $60
Kensington Orbit Wireless Mobile Trackball: 2 buttons, touch surface to scroll, finger ball, $40
Logitech Marble Mouse: 4 buttons, no scroll, $20
Does the Slimblade require drivers? How does the twist motion for scrolling work, is it a natural motion or does it feel awkward?
You need the software they provide to get the 3rd and 4th buttons to work. Scrolling is incredibly natural, but you want to "pivot" instead of twist. You can see in the video review I did here:
http://geekhack.org/showwiki.php?title=Island:25064