Patent ID: 7297441

Claim:
A nonaqueous-electrolyte battery comprising: a unit cell with a capacity (C); and a case accommodating the unit cell, said case comprising at least one plastic film layer A; said case being folded along a plane such that A faces itself thereby forming an opposing section A′; said unit cell being disposed between A and A′; a portion of A and A′ being heat-sealed together along at least a portion of a periphery of said accommodated unit cell; said heat sealed-portion of said case having a thickness (D) of from 20 μm to 200 μm, a moisture vapor permeability (R) as measured on a plastic film layer of thickness (T), an inner peripheral sealing length (L), a cross-sectional area (S) calculated as D×L, and an average heat-sealed portion width (W) of 2 mm to 5 mm; wherein said case has a water penetration rate, as calculated by (T×R×S)/(W×C), of less than 0.96 μg per day per unit capacity of said battery.