Why such a big difference?

It's DIY, though the company, Enginer, is no longer doing private sales (turns out shipping 100kgs of expensive stuff to different countries round the planet is a pain in the arse).

 

There's an additional battery which goes in the place of that black plastic tray in the boot. It can hold 4 kilowatt hours, which is enough for about 15 miles if you can keep it in EV mode, but provides a constant assist while going faster. It's pretty smart, but definitely still a bit DIY. I'm sure the official Toyota setup will be a lot better!

 

Starting an ICE just to maintain it at a min temp is really just the Prius only hybrid model (blended mode) since the ICE is always meant to be available for power when needed. It is really not necessary if the traction motor and battery are engineered to provide sufficient power and energy even at low temps for most short distance travels.

Even more so at higher speeds...

 

Tpfun is trying to make some point about the chevrolet volt being better. sadly he doesn't realise that a) it won't go on sale here as the vauxhall ampera until sometime during 2012 and that b) it will cost $53,000 (£33,000) at launch and c) a lot of company car schemes will exclude it as it's only a four seater.

What actually happens in the prius is your engine warms itself up to a set point (think it's around 70C) and will then allow itself to turn off. it'll stay off until you need power from it OR if you request cabin heat it will cycle on/off as needed. Sometimes you'll notice you stop at a light and the engine doesn't stop. if you hit the off button on the climate control the engine will then shut down - it was only running to keep YOU warm!

With my phev once the engine is warm i can drive until the pack is empty and the engine won't ever come back on, provided i stay in the left area of the HSI and don't exceed 46mph or request cabin heat. there is no change to the prius software, so this would be true for any prius.