BrianG is correct for portable as long as you are in an open enviornment. Stinky motor and carbon monoxide in a close space are not exceptable. Know your application.
I also believe (maybe wrong) that electric power is far less expensive than fossil fuels.
An interesting point you mention is...
Electric motors tend to be 80 percent efficient or better. If you want to make the battery last longer you need to go after the inefficient stuff
Use the law of conservation of energy.
Rather than friction brakes you use reactive brakes.
The spinning magnetic field acts like a generator...
The last person is absolutely correct with a few exception.
No manufacturers data is without massage. Posted low FIT rates are going to be assumed, not necessarily derived. Know your supplier.
Also, remember your application. Some devices have activation points that are below 125C.
Below the...