Range Extender questions?

[mickeyscotty]

Im curious, at what charge % does the range extender kick in, and does it maintain the charge at that level until it basically runs out of fuel?

If so, what is to stop someone from retrofitting a small 5 gal fuel tank for longer trips?

 

[SanSerif]

AIUI, you can fire it up at any point that the battery has the capacity to take some electrons - I've heard 80% mentioned as the max for this but I've also read (here, I think) of the REx running and charging at battery states above this. It will automatically start running at 20% - but you can override this.

The caveat to my understanding is that it is gleamed from reading the web and is based on little in the way of BMW-sourced "facts". Also, it may not be true in all markets; I've heard it said that in the US it can't be manually triggered over 20% charge. If true (and it may well not be) this is probably down to tax breaks and definitions of BEV, PHEV EREV etc etc.

As to what stops you fitting a reserve fuel tank - nothing, I guess. But why? Buy a Ampera or a Volt.