In reading about Envia's claims reagrding their battery breakthrough, I began to wonder about what would happen when it came time to replace my Roadster's batteries. Using the data from this article and others regarding the cost of Tesla's batteries (Tesla wanted to charge a customer $40K for his bricked batteries), I came up with these conclusions: Tesla's battery energy density is 121 watt-hours/kilogram. Envia claims 400 watt-hours/kilogram. Envia claims a cost of $150 per kilowatt-hour. Tesla is about $40K for 53 kilowatt-hours (see above). By my math, the Tesla battery pack would weigh 963 lbs, an equivalent Envia pack would weigh 292 lbs. With Envia's batteries, and keeping the same energy storage level as current batteries (53kwh), I would save about 671 pounds of weight at a cost of $7950 - a savings of about $32K. But how would this weight reduction affect the handling and performance of the Roadster? Would the Roadster's suspension be able to handle the additional performance gains due to the reduced weight and remain balanced? Would the ride be harsher due to the reduced weight? Or I could keep the same weight and have a range of 800+ miles (3.3 times the density of the Tesla batteries times the current range of 245 miles) - but how long would that take to charge? And the cost would be $26,280 for this quantity of batteries. Of course this is all conjecture - these batteries have yet to hit the market and what changes would be required of the Tesla's programming to charge such batteries is unknown at this time. But it's just nice to think of the what-ifs as the price of batteries go down and their density goes up with more research over time.