The ideas below have been posted on many threads, by many members. But now that many now have had more BEV experience and winter is here (I may get to try out my LEAF in the snow for the first time here in North California, tomorrow) I thought maybe there would be interest in a dedicated thread.
I’m still not so ready to totally write off the ICE, as many on this site seem to be.
In fact, a true ICE ”range extender” for a BEV is not a bad Idea, It's just that current designs are all abysmal failures, from the point of energy efficiency and driver utility. Putting an ICE drivetrain in an EV, whether in series, parallel, or any other hybrid configuration, is not advisable, IMO. Invariably, you will get an overweight, overpriced, underperforming vehicle, like the Volt. It seems almost as ridiculous, to install an extremely expensive and heavy large battery pack (like the Tesla S long-range options) which is only occasionally required by the BEV driver.
A functional range extender would consist of:
A small displacement (200-600 CC) ICE generator, run at highest-efficiency rpm, to recharge the battery pack. Generator output would not be sufficient to drive the vehicle, just enough to extend the battery pack range to the next convenient recharge location.
It would not run on gasoline, but a less polluting, and more stable fuel, such as propane (easier refueling) or CNG (lower cost). 5 gallons of Propane, for example, would probably offer about 200 miles of range extention for a LEAF-sized BEV.
The fuel would also be available to a combustion cabin heater, the one use for which battery energy storage is particularly inefficient...