"EV" mode and "B" gear

"B" is engine braking, which has unrelated to electric motor use.

"EV" mode is quite misunderstood, since it has a button and "Stealth" does not. Both are modes where the 60kW electric motor propels the car while the gas engine remains motionless. Both depend on the emission system being heated up already.

The EV maximum is 25 MPH and is invoked by the button.

The Stealth maximum is 45 MPH and is automatic.
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B mode (on shifter) stands for engine braking. You only use this when descending long steep hills/mountains. It will spin the engine without burning fuel to limit speed increase similar to shifting a conventional automatic tranny to L.

EV button is a request to run on battery only IF current conditions allow (state of charge, acceleration requested by driver, etc). Useful for moving across a parking lot, etc. In the 2010, this is available up to 25 mph. (Was 34 mph in Gen II)

Then there is stealth mode in which the engine is stopped just like EV button, but it is the car's ECU (computer), not the EV button that has invoked the condition. In the 2010, this is available up to 45 mph. (Was 41 mph in Gen II) The driver can induce this mode by letting almost off the gas pedal.

Above 45 mph, (exception of warp neutral) the engine has to spin (sometimes without fuel) to protect the motor/generators. When no fuel is used, this is called warp-stealth.

 

You will achieve oneness with the universe when you realize there is no gear, grasshopper.

There are no gears that change in the Prius. Even reverse isn't a gear change. When you reverse you are using the electric motor driven "backwards". Which is why it's hard to reverse in deep mud or up a steep hill.

Well, technically I lie. The "park pawl" that so many worry about is actually a gear that is slid into a mate bolted to the transmission housing. So I guess engaging "P" is "shifting a gear".

 

The EV mode uses the battery only and can be used at low speeds, under 25 mph I think, if there is sufficient charge in the battery. If there isn't enough charge or speed is to high it wont engage and you will get a message telling you it is unavailable.

B mode uses the engine for braking, along with some regeneration. It may be useful if you are descending a long grade and need to use the friction brakes. It will use the engine, with fuel shut off, to help slow the car. This mode is only used infrequently. It's a lot like L or 2 with a conventional automatic transmission. If you depress the throttle while in B the car will perform just as it would in D. If you forget and leave it in B it will shift itself out after some peroid of time.