use B mode to go uphill?

I believe the "B" is for engine braking, not used for acceleration

 

Yes.

Since B mode is only different than D mode while decelerating, you will have no impact going up hill, good or bad. One quirk, no cruise control in B as Toyota is trying to remind you to shift back to D.

(As always, B is a gear you should use like L in an Automatic Transmission, almost never. It can help if you shift to B at the top of a long downhill)

B under the D in the Drive gears? | PriusChat

 

B mode is for downhill braking.

 

It should be fine to do, but there's no reason to do so. You're just wasting gas. B mode uses engine braking to slow the car (for long downhill sections) and is less efficient than normal driving. Just push harder on the gas, it'll be fine

 

B is designed for long downhill descents where constant breaking pressure might cause high heat build up. B uses heavier engine breaking to try to avoid using the friction breaks and emphasizes throwing off that excess heat build up caused by the breaking. It does charge the battery, but not as efficiently as D because B throws away a lot of the energy (the regen meter will still show high because of the engine breaking, but it doesn't account for the lost energy). Basically B is less energy efficient than D and should not be used unless you are making an extremely long downhill descent, such as a person who lives in a mountainous region would.