coasting

In either mode, EV or HV, coasting will regenerate power to the battery if your foot is not applying any power at all and the indicator on the MID display is "below the line" in the charge section of the graph. Page 210 of your manual.

 

Yes... you have lots of things being powered (the dash, navigation, various body and engine computers, etc.). There's no way to turn off all the power and still have the car rolling (even the break and steering systems use electric motors).

 

To give you a more technical answer. Yes, coasting in my opinion is better than riding the brakes in most situations, at least for me. In the Prime when you coast you're charging the battery around ~20 A (figure about 350-360 volts, around 7,000 watts). Depending on how hard your AC/Heat Pump is working current drawn by my observations can be nill (less than 1 A) to as high as 7-8 A, so you're still getting a fairly good charge.

When it comes to regenerative braking on the prime I've seen a peak up to around 108 A. The limit is 40 kW, this is up from 32 kW on the regular NiMH 4th gen Prius.

The power is never really off, the car has the ability to switch the direction of electrical current as needed. If more is coming in than being consumed that power goes back into the battery. However, there are inefficiencies, tires, electronics....heat is a big one. So the less fiddling you're doing with the pedals the better. If you know you're going to stop, braking lightly and early is best -- just don't piss people off braking 3/4 mile away from the next traffic light during rush hour.

I guess getting back to your answer, it would be very difficult to create a condition where you're drawing more than 6,000-7,000 watt load and coasting. You can have the radio cranked, high beams on, rear defroster going and the AC on low... I think the 12 volt charging system is rated for 100 amps and assuming you can get 13.8 volts at 100 A that's still only 1,380 watts.

The hybrid system is able to output around ~67 kW in EV mode (the max output dips into the ~50 kW area when depleted in HV mode, but don't expect to get a full 50 kW, going to be more like a regular Prius in HV mode so would realistically get around 21 kW when giving it the beans.

If you have a OBDII scanner look at WIN CONTROL LIMIT POWER (power input, charging) and WOUT CONTROL LIMIT POWER (power output), there's also PID's for Hybrid Battery Current and Hybrid Battery Voltage (total of all 95 cells) which with that you can get a good idea of just how much is going in and going out.

The nice thing if you have a Prime and you're about to go down a big mountain, you can regen all you want, unlike a regular Prius where the battery gets fully charged in a 1 mile or so, if you got 5 miles...10 miles, you can regenerate all you want (provided the battery temps and other components don't get too hot -- if you watch that WIN CONTROL POWER pid it will go down if something gets too hot, too cold, battery is fully charged, etc).

Anyway, hope this helps explain what's going on. There might be others who can comment on the technical aspect with more detail.