Hi Trevor,
Sounds like a great idea to me, and if you could demonstrate a 20 mile plug-in range Prius, I'm pretty sure Toyota would also be really keen to see that working (and maybe give them some good ideas for Prius 3, hint hint!). Wouldn't it be great if the first plug-in hybrids on the road were amateur conversions like this?
Anyway, as for battery options you have several:
1) NiMH
You could simply put in parallel an extra NiMH pack of the same type already used in your 2004. They are made by Panasonic EV (see
here), and have about
46Wh/kg, but given the huge demand for them right now (not just for Prius, but all the other coming hybrids), the chance of a private individual like yourself managing to buy one either from them or from your local Toyota parts department is probably next to negligible right now!
Alternatively, you could maybe buy some of the packs they made for the RAV4 EV. THey're designed for much deeper charge/discharge cycles, and at
65Wh/kg would be much better for range extending purposes. As the RAV4 EV has been canned, they might even be available too, though they will be expensive.
2) Lead acid
Don't do it!
35Wh/kg at best would mean a very heavy Prius for a very modest range (figure on about 4 miles range per kWh storage).
3) Thundersky Lithium Ion
Now we're talking!
140Wh/kg, readily available to the amateur (see
here) at about
$200 per kWh. A 50 kilo pack in the boot wouldn't take up too much space, and with 7kWh would give you a plug-in-electric range of about
28 miles - enough for many people's commutes.
4) 18650 Lithium Ion
Or, for the same numbers, you could try taking the 18650 route. These are the small cylindrical ~AA sized batteries used to make up camera and laptop batteries. (Roughly on a par with the thundersky on cost, off the shelf availability and energy density). The only difference is that these would be more fiddly to use. The 28 mile EV range would require you to build a pack made up of about 1,200 individual cells, just as AC propulsion have done to such
great effect!
5) Lithium Sulphur
OK, so you can't buy these just yet! But with
350Wh/kg storage already
demonstrated by SION for laptop batteries, a 100kg LiS battery in the boot would give you an all electric range of up to
140 miles before the ICE engine even needs to start up. Come on Toyota, drop this fuel cell crap and DO A DEAL WITH SION!!!!
