Plug-In Supply Inc. has just introduced a $4,995 Toyota Prius plug-in conversion kit which uses a pack of twenty PbA20-12 lead-acid batteries. Good for 5kWh, the battery pack should last more than 800 charge cycles, or about two years. As you would expect from something with the word "lead" in it, the batteries weigh 360 lbs — over twice as much as the standard batteries on a Prius. But the system does make it possible to drive a deadly silent 10-15 miles on pure electric power and achieve mileage of up to 100 MPG. So, is this the ultimate Prius?

If you're interested in something a bit more modern, the system is designed to work with an upgrade to lithium iron phosphate batteries too. And if you want to pump juice into those batteries using nothing but the sun, you might want to bolt on some solar panels. Us? We'd still rather have a VW Golf Twin Drive. [GreenCarCongress]