[Mkalman115]

When battery runs down to “0 miles” charge, which mode is more fuel efficient… D or B?

 

[r.elegante]

When battery runs down to “0 miles” charge, which mode is more fuel efficient… D or B?

B mode is more efficient. In B mode you will put some charge back in the battery when you use the resistance braking. Sometime I get 7 or 8 "miles" that way. Then the system can use that extra electricity. In D you are just wearing down the brake pads with no energy gain. Both modes are using the brake pads when you press the brake pedal. I use B mode 99% of the time. (But put it in D before you pull up to a car wash or the brakes will cause problems)

 

[Mkalman115]

I thought that was the case, but it's not intuitively ovious. There is a perceptable increase is resistance when B mode is started, and the engine seems to be straining a bit more. On a recent 150 mile trip, stating with no miles on the battery, I was in D for the first 100 miles, and MPG was just over 30. At the end of the trip, MPG had crept up to 31.5. Seems to prove your point, although there were lots of other variables. (Not all highway in the beginning.)

 

[r.elegante]

I thought that was the case, but it's not intuitively ovious. There is a perceptable increase is resistance when B mode is started, and the engine seems to be straining a bit more. On a recent 150 mile trip, stating with no miles on the battery, I was in D for the first 100 miles, and MPG was just over 30. At the end of the trip, MPG had crept up to 31.5. Seems to prove your point, although there were lots of other variables. (Not all highway in the beginning.)

You may also notice that in B mode at a traffic light with 0 miles the car will start off in electrical before quickly changing to gas. B mode won't do much for you on flat highways with a relative constant highway speeds as there isn't a lot of braking. It is a lot more beneficial in town assuming you planning a bit ahead and not hitting the brake pedal much.