Lifetime cycles are an issue for Li-ion batteries.<p>For example, lets look at the Tesla Powerwall numbers.  The Powerwall warranty covers 85% of capacity with 740 cycles in the first two years -- whichever comes first. Then it covers 66% capacity with 1,087 cycles in three years, and finally, it covers 54% of capacity for 2,368 cycles in five years. <a href="http:&#x2F;&#x2F;www.greentechmedia.com&#x2F;articles&#x2F;read&#x2F;is-teslas-powerwall-luster-already-fading" rel="nofollow">http:&#x2F;&#x2F;www.greentechmedia.com&#x2F;articles&#x2F;read&#x2F;is-teslas-powerw...</a><p>Running the numbers for the Powerwall, 85%, 66%, and 54% of 7kWh is 5.4, 4.6, and 3.8kWh respectively.<p>(740cycles x 5.4kWh) + (1087cycles x 4.6kWh) + (2368cycles x 3.8kWh) = 17994.6kWh<p>Thus the cost per kWh stored is<p>$3000&#x2F;17994.6kWh = 16.7 cents&#x2F;kWh.<p>Not included is the shipping and installation cost, which could add another $300 - $500, which would run<p>$3300&#x2F;17994.6kWh = 18.3 cent&#x2F;kWh.