Charge Mode ONLY mpg

As others have tried to communicate and have said, there is not an official average number when using charge mode. EPA doesn't require it, because it's not a "standard" mode. My assumption is that they test "as the car froms from the factory" to give the official milage. For example, the car is likely in Normal vs Eco or Performance driving mode.

There are significant effeiciency loses when burnging gasoline to charge the battery, just like the regneerative breaking doesn't give you 100% of the energy you used to accelerate the car.

If you search the forums here, you will see this issue has been discussed a number of times. People have given some estimates, but it is highly variable and no matter what, efficiency will be worse than not using charge mode. If you do some experiments, please report back, I'm curious too--but not curious enough to run my own experiments (e.g. "car sitting in the driveway in 50F weather, in charge mode, how much gasoline does it burn to go from hybrid mode to a full charge", or similar).

 

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Someone posted the driveway experiment thing to one of these Charge Mode or Prius Camping threads.
It wasn't pretty, but iirc it wasn't as bad as my example in #11

The other issue is that many Prime owners try charge mode once or twice without knowing anything about how it works, and seeing the MPG results declare it as a Useless feature and worse. And one of the threads got into a B mode discussion that lasted for 5 or 10 pages and seemed to never end even after a few tries were made to point it back towards a charge mode discussion.

I get kind of suspicious when I see a request for info and continuous complaints from the OP about the way others are responding to a post.