Have you not been reading this thread? I never said anything about performance degradation with extreme temperature, if for no other reason, I am well aware that few yacht interiors ever reach -20C. I merely stated that 15C is the figure used to illustrate self discharge rates and 15C is not extreme. Please don't try to make it look like I even bothered to discuss battery performance at any temperature. I don't think it is a factor even if they were a viable option for large yacht propulsion, which I don't think they will by by 2015 or even 2020. This thread is about yachts, yachts are designed to be mobile. Geothermal sources are not available at sea, and long extension cords are unwieldy. like I wrote earlier, show me a 3 megawatt battery and charging system that doen't require stopping for a week every few miles on the way to St. Maarten. Few Caribbean islands have solar or geothermal power supplies on their grid. Most are powered by diesel or steam, and burn fossil fuels. Recharging yacht batteries only tranfers the cost and pollution to people and facilities already reeling from declining local economies and rising energy prices. At around $6 million per megawatt, we are unlikely to see yachts fitted with 3 or 4 megawatts of solar arrays. I can't be bothered to do the math for you but it would probably require an array the size of an aircraft carrier flight deck to keep the yacht moving.