Does the Ryobi P262 come with a battery?

No. It is sold as a bare tool, so you need an 18V ONE+ battery and charger. Any ONE+ pack works, though a 4 Ah or larger pack suits the high current draw.

Is 600 ft-lbs enough for lug nuts?

Yes for most passenger cars and light trucks, whose lug nuts are typically tightened to well under 150 ft-lbs. Very stubborn or rusted fasteners on heavy trucks may need a breaker bar or a higher-torque wrench.

What is the difference between breakaway and fastening torque?

Breakaway torque is the peak it can deliver to loosen a stuck fastener. Fastening torque is the lower sustained figure for tightening, so use a torque wrench for final lug-nut torque.

Does it use a pin detent or friction ring?

It uses a 1/2-inch friction-ring anvil. Sockets push on and are held by friction, so check them before use, especially overhead.

How does it compare with the Ryobi P261?

The P262 is the HP brushless high-torque model with more breakaway torque and four speed modes. The P261 is the older, lower-torque mid-range wrench and is lighter and less expensive.