I think you are in error in you value for lead acid battery storage capacity. http://en.wikipedia.org/wiki/Lithium-ion_polymer_battery The link is of a Li-ploy battery which is 1/3 the weight of a lead acid for a given capacity.
They show 130-200 Whr per KG of battery weight.
That is consistant with my experience in flying electric RC planes with a Li-poly battery.
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